Using Microsoft Visual FoxPro 9, I have a custom function, "newid()", inside of the stored procedures for Main:
function newId
parameter thisdbf
regional keynm, newkey, cOldSelect, lDone
keynm=padr(upper(thisdbf),50)
cOldSelect=alias()
lDone=.f.
do while not lDone
select keyvalue from main!idkeys where keyname=keynm into array akey
if _tally=0
insert into main!idkeys (keyname) value (keynm)
loop
endif
newkey=akey+1
update main!idkeys set keyvalue=newkey where keyname=keynm and keyvalue=akey
if _tally=1
lDone=.t.
endif
enddo
if not empty(cOldSelect)
select &cOldSelect
else
select 0
endif
return newkey
This function is used to generate a new ID for records added to the database.
It is called as the default value:
I would like to call this newid() function and retrieve its returned value. When executing SELECT newid("TABLENAME"), the error is is thrown:
Invalid subscript reference
How can I call the newid() function and return the newkey in Visual FoxPro 9?
As an addition to what Stefan Wuebbe said,
You actually had your answer in your previous question here that you forgot to update.
From your previous question, as I understand you are coming from a T-SQL background. While in T-SQL (and in SQL generally) there is:
Select < anyVariableOrFunction >
that returns a single column, single row result, in VFP 'select' like that has another meaning:
Select < aliasName >
aliasName is an alias of a working area (or it could be number of a work area) and is used to change the 'current workarea'. When it was used in xBase languages like FoxPro (and dBase), those languages didn't yet meet ANSI-SQL if I am not wrong. Anyway, in VFP there are two Select, this one and SELECT—SQL which definitely requires a FROM clause.
VFP has direct access to variables and function calls though, through the use of = operator.
SELECT newid("TABLENAME")
in T-SQL, would be (you are just displaying the result):
? newid("TABLENAME")
To store it in a variable, you would do something like:
local lnId
lnId = newid("TABLENAME")
* do something with m.lnId
* Note the m. prefix, it is a built-in alias for memory variables
After having said all these, as per your code.
It looks like it has been written by a very old FoxPro programmer and I must admit I am seeing it the first time in my life that someone used "REGIONAL" keyword in VFP. It is from FoxPro 2.x days I know but I didn't see anyone use it up until now :) Anyway, that code doesn't seem to be robust enough in a multiuser environment, you might want to change it. VFP ships with a NewId sample code and below is the slightly modified version that I have been using in many locations and proved to be reliable:
Function NewID
Lparameters tcAlias,tnCount
Local lcAlias, lnOldArea, lcOldReprocess, lcTable, lnTagNo, lnNewValue, lnLastValue, lcOldSetDeleted
lnOldArea = Select()
lnOldReprocess = Set('REPROCESS')
* Uppercase Alias name
lcAlias = Upper(Iif(Parameters() = 0, Alias(), tcAlias))
* Lock reprocess - try once
Set Reprocess To 1
If !Used("IDS")
Use ids In 0
Endif
* If no entry yet create
If !Seek(lcAlias, "Ids", "tablename")
Insert Into ids (tablename, NextID) Values (lcAlias,0)
Endif
* Lock, increment id, unlock, return nextid value
Do While !Rlock('ids')
* Delay before next lock trial
lnStart = Seconds()
Do While Seconds()-lnStart < 0.01
Enddo
Enddo
lnLastValue = ids.NextID
lnNewValue = m.lnLastValue + Evl(m.tnCount,1)
*Try to query primary key tag for lcAlias
lcTable = Iif( Used(lcAlias),Dbf(lcAlias), Iif(File(lcAlias+'.dbf'),lcAlias,''))
lcTable = Evl(m.lcTable,m.lcAlias)
If !Empty(lcTable)
Use (lcTable) In 0 Again Alias '_GetPKKey_'
For m.lnTagNo=1 To Tagcount('','_GetPKKey_')
If Primary(m.lnTagNo,'_GetPKKey_')
m.lcOldSetDeleted = Set("Deleted")
Set Deleted Off
Select '_GetPKKey_'
Set Order To Tag (Tag(m.lnTagNo,'_GetPKKey_')) ;
In '_GetPKKey_' Descending
Locate
lnLastValue = Max(m.lnLastValue, Evaluate(Key(m.lnTagNo,'_GetPKKey_')))
lnNewValue = m.lnLastValue + Evl(m.tnCount,1)
If Upper(m.lcOldSetDeleted) == 'ON'
Set Deleted On
Endif
Exit
Endif
Endfor
Use In '_GetPKKey_'
Select ids
Endif
* Increment
Replace ids.NextID With m.lnNewValue In 'ids'
Unlock In 'ids'
Select (lnOldArea)
Set Reprocess To lnOldReprocess
Return ids.NextID
Endfunc
Note: If you use this, as I see from your code, you would need to change the "id table" name to idkeys, field names to keyname, keyvalue:
ids => idKeys
tablename => keyName
nextId => keyValue
Or in your database just create a new table with this code:
CREATE TABLE ids (TableName c(50), NextId i)
INDEX on TableName TAG TableName
When executing SELECT newid("TABLENAME")
The error: Invalid subscript reference is thrown
The SQL Select command in Vfp requires a From clause.
Running a procedure or a function can, or better usually needs to be done differently:
For example, in the IDE's Command Window you can do a
? newid("xy") && the function must be "in scope",
&& i.e in your case the database that contains the "Stored
&& Procedure" must have been opened in advance
&& or you store the function result in a variable
Local lnNextID
lnNextID = newid("xy")
Or you can use it in an SQL SELECT when you have a From alias
CREATE CURSOR placebo (col1 Int)
INSERT INTO placebo VALUES (8)
Select newid("xy") FROM placebo
What are the best workarounds for using a SQL IN clause with instances of java.sql.PreparedStatement, which is not supported for multiple values due to SQL injection attack security issues: One ? placeholder represents one value, rather than a list of values.
Consider the following SQL statement:
SELECT my_column FROM my_table where search_column IN (?)
Using preparedStatement.setString( 1, "'A', 'B', 'C'" ); is essentially a non-working attempt at a workaround of the reasons for using ? in the first place.
What workarounds are available?
An analysis of the various options available, and the pros and cons of each is available in Jeanne Boyarsky's Batching Select Statements in JDBC entry on JavaRanch Journal.
The suggested options are:
Prepare SELECT my_column FROM my_table WHERE search_column = ?, execute it for each value and UNION the results client-side. Requires only one prepared statement. Slow and painful.
Prepare SELECT my_column FROM my_table WHERE search_column IN (?,?,?) and execute it. Requires one prepared statement per size-of-IN-list. Fast and obvious.
Prepare SELECT my_column FROM my_table WHERE search_column = ? ; SELECT my_column FROM my_table WHERE search_column = ? ; ... and execute it. [Or use UNION ALL in place of those semicolons. --ed] Requires one prepared statement per size-of-IN-list. Stupidly slow, strictly worse than WHERE search_column IN (?,?,?), so I don't know why the blogger even suggested it.
Use a stored procedure to construct the result set.
Prepare N different size-of-IN-list queries; say, with 2, 10, and 50 values. To search for an IN-list with 6 different values, populate the size-10 query so that it looks like SELECT my_column FROM my_table WHERE search_column IN (1,2,3,4,5,6,6,6,6,6). Any decent server will optimize out the duplicate values before running the query.
None of these options are ideal.
The best option if you are using JDBC4 and a server that supports x = ANY(y), is to use PreparedStatement.setArray as described in Boris's anwser.
There doesn't seem to be any way to make setArray work with IN-lists, though.
Sometimes SQL statements are loaded at runtime (e.g., from a properties file) but require a variable number of parameters. In such cases, first define the query:
query=SELECT * FROM table t WHERE t.column IN (?)
Next, load the query. Then determine the number of parameters prior to running it. Once the parameter count is known, run:
sql = any( sql, count );
For example:
/**
* Converts a SQL statement containing exactly one IN clause to an IN clause
* using multiple comma-delimited parameters.
*
* #param sql The SQL statement string with one IN clause.
* #param params The number of parameters the SQL statement requires.
* #return The SQL statement with (?) replaced with multiple parameter
* placeholders.
*/
public static String any(String sql, final int params) {
// Create a comma-delimited list based on the number of parameters.
final StringBuilder sb = new StringBuilder(
String.join(", ", Collections.nCopies(possibleValue.size(), "?")));
// For more than 1 parameter, replace the single parameter with
// multiple parameter placeholders.
if (sb.length() > 1) {
sql = sql.replace("(?)", "(" + sb + ")");
}
// Return the modified comma-delimited list of parameters.
return sql;
}
For certain databases where passing an array via the JDBC 4 specification is unsupported, this method can facilitate transforming the slow = ? into the faster IN (?) clause condition, which can then be expanded by calling the any method.
Solution for PostgreSQL:
final PreparedStatement statement = connection.prepareStatement(
"SELECT my_column FROM my_table where search_column = ANY (?)"
);
final String[] values = getValues();
statement.setArray(1, connection.createArrayOf("text", values));
try (ResultSet rs = statement.executeQuery()) {
while(rs.next()) {
// do some...
}
}
or
final PreparedStatement statement = connection.prepareStatement(
"SELECT my_column FROM my_table " +
"where search_column IN (SELECT * FROM unnest(?))"
);
final String[] values = getValues();
statement.setArray(1, connection.createArrayOf("text", values));
try (ResultSet rs = statement.executeQuery()) {
while(rs.next()) {
// do some...
}
}
No simple way AFAIK.
If the target is to keep statement cache ratio high (i.e to not create a statement per every parameter count), you may do the following:
create a statement with a few (e.g. 10) parameters:
... WHERE A IN (?,?,?,?,?,?,?,?,?,?) ...
Bind all actuall parameters
setString(1,"foo");
setString(2,"bar");
Bind the rest as NULL
setNull(3,Types.VARCHAR)
...
setNull(10,Types.VARCHAR)
NULL never matches anything, so it gets optimized out by the SQL plan builder.
The logic is easy to automate when you pass a List into a DAO function:
while( i < param.size() ) {
ps.setString(i+1,param.get(i));
i++;
}
while( i < MAX_PARAMS ) {
ps.setNull(i+1,Types.VARCHAR);
i++;
}
You can use Collections.nCopies to generate a collection of placeholders and join them using String.join:
List<String> params = getParams();
String placeHolders = String.join(",", Collections.nCopies(params.size(), "?"));
String sql = "select * from your_table where some_column in (" + placeHolders + ")";
try ( Connection connection = getConnection();
PreparedStatement ps = connection.prepareStatement(sql)) {
int i = 1;
for (String param : params) {
ps.setString(i++, param);
}
/*
* Execute query/do stuff
*/
}
An unpleasant work-around, but certainly feasible is to use a nested query. Create a temporary table MYVALUES with a column in it. Insert your list of values into the MYVALUES table. Then execute
select my_column from my_table where search_column in ( SELECT value FROM MYVALUES )
Ugly, but a viable alternative if your list of values is very large.
This technique has the added advantage of potentially better query plans from the optimizer (check a page for multiple values, tablescan only once instead once per value, etc) may save on overhead if your database doesn't cache prepared statements. Your "INSERTS" would need to be done in batch and the MYVALUES table may need to be tweaked to have minimal locking or other high-overhead protections.
Limitations of the in() operator is the root of all evil.
It works for trivial cases, and you can extend it with "automatic generation of the prepared statement" however it is always having its limits.
if you're creating a statement with variable number of parameters, that will make an sql parse overhead at each call
on many platforms, the number of parameters of in() operator are limited
on all platforms, total SQL text size is limited, making impossible for sending down 2000 placeholders for the in params
sending down bind variables of 1000-10k is not possible, as the JDBC driver is having its limitations
The in() approach can be good enough for some cases, but not rocket proof :)
The rocket-proof solution is to pass the arbitrary number of parameters in a separate call (by passing a clob of params, for example), and then have a view (or any other way) to represent them in SQL and use in your where criteria.
A brute-force variant is here http://tkyte.blogspot.hu/2006/06/varying-in-lists.html
However if you can use PL/SQL, this mess can become pretty neat.
function getCustomers(in_customerIdList clob) return sys_refcursor is
begin
aux_in_list.parse(in_customerIdList);
open res for
select *
from customer c,
in_list v
where c.customer_id=v.token;
return res;
end;
Then you can pass arbitrary number of comma separated customer ids in the parameter, and:
will get no parse delay, as the SQL for select is stable
no pipelined functions complexity - it is just one query
the SQL is using a simple join, instead of an IN operator, which is quite fast
after all, it is a good rule of thumb of not hitting the database with any plain select or DML, since it is Oracle, which offers lightyears of more than MySQL or similar simple database engines. PL/SQL allows you to hide the storage model from your application domain model in an effective way.
The trick here is:
we need a call which accepts the long string, and store somewhere where the db session can access to it (e.g. simple package variable, or dbms_session.set_context)
then we need a view which can parse this to rows
and then you have a view which contains the ids you're querying, so all you need is a simple join to the table queried.
The view looks like:
create or replace view in_list
as
select
trim( substr (txt,
instr (txt, ',', 1, level ) + 1,
instr (txt, ',', 1, level+1)
- instr (txt, ',', 1, level) -1 ) ) as token
from (select ','||aux_in_list.getpayload||',' txt from dual)
connect by level <= length(aux_in_list.getpayload)-length(replace(aux_in_list.getpayload,',',''))+1
where aux_in_list.getpayload refers to the original input string.
A possible approach would be to pass pl/sql arrays (supported by Oracle only), however you can't use those in pure SQL, therefore a conversion step is always needed. The conversion can not be done in SQL, so after all, passing a clob with all parameters in string and converting it witin a view is the most efficient solution.
Here's how I solved it in my own application. Ideally, you should use a StringBuilder instead of using + for Strings.
String inParenthesis = "(?";
for(int i = 1;i < myList.size();i++) {
inParenthesis += ", ?";
}
inParenthesis += ")";
try(PreparedStatement statement = SQLite.connection.prepareStatement(
String.format("UPDATE table SET value='WINNER' WHERE startTime=? AND name=? AND traderIdx=? AND someValue IN %s", inParenthesis))) {
int x = 1;
statement.setLong(x++, race.startTime);
statement.setString(x++, race.name);
statement.setInt(x++, traderIdx);
for(String str : race.betFair.winners) {
statement.setString(x++, str);
}
int effected = statement.executeUpdate();
}
Using a variable like x above instead of concrete numbers helps a lot if you decide to change the query at a later time.
I've never tried it, but would .setArray() do what you're looking for?
Update: Evidently not. setArray only seems to work with a java.sql.Array that comes from an ARRAY column that you've retrieved from a previous query, or a subquery with an ARRAY column.
My workaround is:
create or replace type split_tbl as table of varchar(32767);
/
create or replace function split
(
p_list varchar2,
p_del varchar2 := ','
) return split_tbl pipelined
is
l_idx pls_integer;
l_list varchar2(32767) := p_list;
l_value varchar2(32767);
begin
loop
l_idx := instr(l_list,p_del);
if l_idx > 0 then
pipe row(substr(l_list,1,l_idx-1));
l_list := substr(l_list,l_idx+length(p_del));
else
pipe row(l_list);
exit;
end if;
end loop;
return;
end split;
/
Now you can use one variable to obtain some values in a table:
select * from table(split('one,two,three'))
one
two
three
select * from TABLE1 where COL1 in (select * from table(split('value1,value2')))
value1 AAA
value2 BBB
So, the prepared statement could be:
"select * from TABLE where COL in (select * from table(split(?)))"
Regards,
Javier Ibanez
I suppose you could (using basic string manipulation) generate the query string in the PreparedStatement to have a number of ?'s matching the number of items in your list.
Of course if you're doing that you're just a step away from generating a giant chained OR in your query, but without having the right number of ? in the query string, I don't see how else you can work around this.
You could use setArray method as mentioned in this javadoc:
PreparedStatement statement = connection.prepareStatement("Select * from emp where field in (?)");
Array array = statement.getConnection().createArrayOf("VARCHAR", new Object[]{"E1", "E2","E3"});
statement.setArray(1, array);
ResultSet rs = statement.executeQuery();
Here's a complete solution in Java to create the prepared statement for you:
/*usage:
Util u = new Util(500); //500 items per bracket.
String sqlBefore = "select * from myTable where (";
List<Integer> values = new ArrayList<Integer>(Arrays.asList(1,2,4,5));
string sqlAfter = ") and foo = 'bar'";
PreparedStatement ps = u.prepareStatements(sqlBefore, values, sqlAfter, connection, "someId");
*/
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
public class Util {
private int numValuesInClause;
public Util(int numValuesInClause) {
super();
this.numValuesInClause = numValuesInClause;
}
public int getNumValuesInClause() {
return numValuesInClause;
}
public void setNumValuesInClause(int numValuesInClause) {
this.numValuesInClause = numValuesInClause;
}
/** Split a given list into a list of lists for the given size of numValuesInClause*/
public List<List<Integer>> splitList(
List<Integer> values) {
List<List<Integer>> newList = new ArrayList<List<Integer>>();
while (values.size() > numValuesInClause) {
List<Integer> sublist = values.subList(0,numValuesInClause);
List<Integer> values2 = values.subList(numValuesInClause, values.size());
values = values2;
newList.add( sublist);
}
newList.add(values);
return newList;
}
/**
* Generates a series of split out in clause statements.
* #param sqlBefore ""select * from dual where ("
* #param values [1,2,3,4,5,6,7,8,9,10]
* #param "sqlAfter ) and id = 5"
* #return "select * from dual where (id in (1,2,3) or id in (4,5,6) or id in (7,8,9) or id in (10)"
*/
public String genInClauseSql(String sqlBefore, List<Integer> values,
String sqlAfter, String identifier)
{
List<List<Integer>> newLists = splitList(values);
String stmt = sqlBefore;
/* now generate the in clause for each list */
int j = 0; /* keep track of list:newLists index */
for (List<Integer> list : newLists) {
stmt = stmt + identifier +" in (";
StringBuilder innerBuilder = new StringBuilder();
for (int i = 0; i < list.size(); i++) {
innerBuilder.append("?,");
}
String inClause = innerBuilder.deleteCharAt(
innerBuilder.length() - 1).toString();
stmt = stmt + inClause;
stmt = stmt + ")";
if (++j < newLists.size()) {
stmt = stmt + " OR ";
}
}
stmt = stmt + sqlAfter;
return stmt;
}
/**
* Method to convert your SQL and a list of ID into a safe prepared
* statements
*
* #throws SQLException
*/
public PreparedStatement prepareStatements(String sqlBefore,
ArrayList<Integer> values, String sqlAfter, Connection c, String identifier)
throws SQLException {
/* First split our potentially big list into lots of lists */
String stmt = genInClauseSql(sqlBefore, values, sqlAfter, identifier);
PreparedStatement ps = c.prepareStatement(stmt);
int i = 1;
for (int val : values)
{
ps.setInt(i++, val);
}
return ps;
}
}
Spring allows passing java.util.Lists to NamedParameterJdbcTemplate , which automates the generation of (?, ?, ?, ..., ?), as appropriate for the number of arguments.
For Oracle, this blog posting discusses the use of oracle.sql.ARRAY (Connection.createArrayOf doesn't work with Oracle). For this you have to modify your SQL statement:
SELECT my_column FROM my_table where search_column IN (select COLUMN_VALUE from table(?))
The oracle table function transforms the passed array into a table like value usable in the IN statement.
try using the instr function?
select my_column from my_table where instr(?, ','||search_column||',') > 0
then
ps.setString(1, ",A,B,C,");
Admittedly this is a bit of a dirty hack, but it does reduce the opportunities for sql injection. Works in oracle anyway.
Sormula supports SQL IN operator by allowing you to supply a java.util.Collection object as a parameter. It creates a prepared statement with a ? for each of the elements the collection. See Example 4 (SQL in example is a comment to clarify what is created but is not used by Sormula).
Generate the query string in the PreparedStatement to have a number of ?'s matching the number of items in your list. Here's an example:
public void myQuery(List<String> items, int other) {
...
String q4in = generateQsForIn(items.size());
String sql = "select * from stuff where foo in ( " + q4in + " ) and bar = ?";
PreparedStatement ps = connection.prepareStatement(sql);
int i = 1;
for (String item : items) {
ps.setString(i++, item);
}
ps.setInt(i++, other);
ResultSet rs = ps.executeQuery();
...
}
private String generateQsForIn(int numQs) {
String items = "";
for (int i = 0; i < numQs; i++) {
if (i != 0) items += ", ";
items += "?";
}
return items;
}
instead of using
SELECT my_column FROM my_table where search_column IN (?)
use the Sql Statement as
select id, name from users where id in (?, ?, ?)
and
preparedStatement.setString( 1, 'A');
preparedStatement.setString( 2,'B');
preparedStatement.setString( 3, 'C');
or use a stored procedure this would be the best solution, since the sql statements will be compiled and stored in DataBase server
I came across a number of limitations related to prepared statement:
The prepared statements are cached only inside the same session (Postgres), so it will really work only with connection pooling
A lot of different prepared statements as proposed by #BalusC may cause the cache to overfill and previously cached statements will be dropped
The query has to be optimized and use indices. Sounds obvious, however e.g. the ANY(ARRAY...) statement proposed by #Boris in one of the top answers cannot use indices and query will be slow despite caching
The prepared statement caches the query plan as well and the actual values of any parameters specified in the statement are unavailable.
Among the proposed solutions I would choose the one that doesn't decrease the query performance and makes the less number of queries. This will be the #4 (batching few queries) from the #Don link or specifying NULL values for unneeded '?' marks as proposed by #Vladimir Dyuzhev
SetArray is the best solution but its not available for many older drivers. The following workaround can be used in java8
String baseQuery ="SELECT my_column FROM my_table where search_column IN (%s)"
String markersString = inputArray.stream().map(e -> "?").collect(joining(","));
String sqlQuery = String.format(baseSQL, markersString);
//Now create Prepared Statement and use loop to Set entries
int index=1;
for (String input : inputArray) {
preparedStatement.setString(index++, input);
}
This solution is better than other ugly while loop solutions where the query string is built by manual iterations
I just worked out a PostgreSQL-specific option for this. It's a bit of a hack, and comes with its own pros and cons and limitations, but it seems to work and isn't limited to a specific development language, platform, or PG driver.
The trick of course is to find a way to pass an arbitrary length collection of values as a single parameter, and have the db recognize it as multiple values. The solution I have working is to construct a delimited string from the values in the collection, pass that string as a single parameter, and use string_to_array() with the requisite casting for PostgreSQL to properly make use of it.
So if you want to search for "foo", "blah", and "abc", you might concatenate them together into a single string as: 'foo,blah,abc'. Here's the straight SQL:
select column from table
where search_column = any (string_to_array('foo,blah,abc', ',')::text[]);
You would obviously change the explicit cast to whatever you wanted your resulting value array to be -- int, text, uuid, etc. And because the function is taking a single string value (or two I suppose, if you want to customize the delimiter as well), you can pass it as a parameter in a prepared statement:
select column from table
where search_column = any (string_to_array($1, ',')::text[]);
This is even flexible enough to support things like LIKE comparisons:
select column from table
where search_column like any (string_to_array('foo%,blah%,abc%', ',')::text[]);
Again, no question it's a hack, but it works and allows you to still use pre-compiled prepared statements that take *ahem* discrete parameters, with the accompanying security and (maybe) performance benefits. Is it advisable and actually performant? Naturally, it depends, as you've got string parsing and possibly casting going on before your query even runs. If you're expecting to send three, five, a few dozen values, sure, it's probably fine. A few thousand? Yeah, maybe not so much. YMMV, limitations and exclusions apply, no warranty express or implied.
But it works.
No one else seems to have suggested using an off-the-shelf query builder yet, like jOOQ or QueryDSL or even Criteria Query that manage dynamic IN lists out of the box, possibly including the management of all edge cases that may arise, such as:
Running into Oracle's maximum of 1000 elements per IN list (irrespective of the number of bind values)
Running into any driver's maximum number of bind values, which I've documented in this answer
Running into cursor cache contention problems because too many distinct SQL strings are "hard parsed" and execution plans cannot be cached anymore (jOOQ and since recently also Hibernate work around this by offering IN list padding)
(Disclaimer: I work for the company behind jOOQ)
Just for completeness: So long as the set of values is not too large, you could also simply string-construct a statement like
... WHERE tab.col = ? OR tab.col = ? OR tab.col = ?
which you could then pass to prepare(), and then use setXXX() in a loop to set all the values. This looks yucky, but many "big" commercial systems routinely do this kind of thing until they hit DB-specific limits, such as 32 KB (I think it is) for statements in Oracle.
Of course you need to ensure that the set will never be unreasonably large, or do error trapping in the event that it is.
Following Adam's idea. Make your prepared statement sort of select my_column from my_table where search_column in (#)
Create a String x and fill it with a number of "?,?,?" depending on your list of values
Then just change the # in the query for your new String x an populate
There are different alternative approaches that we can use for IN clause in PreparedStatement.
Using Single Queries - slowest performance and resource intensive
Using StoredProcedure - Fastest but database specific
Creating dynamic query for PreparedStatement - Good Performance but doesn't get benefit of caching and PreparedStatement is recompiled every time.
Use NULL in PreparedStatement queries - Optimal performance, works great when you know the limit of IN clause arguments. If there is no limit, then you can execute queries in batch.
Sample code snippet is;
int i = 1;
for(; i <=ids.length; i++){
ps.setInt(i, ids[i-1]);
}
//set null for remaining ones
for(; i<=PARAM_SIZE;i++){
ps.setNull(i, java.sql.Types.INTEGER);
}
You can check more details about these alternative approaches here.
For some situations regexp might help.
Here is an example I've checked on Oracle, and it works.
select * from my_table where REGEXP_LIKE (search_column, 'value1|value2')
But there is a number of drawbacks with it:
Any column it applied should be converted to varchar/char, at least implicitly.
Need to be careful with special characters.
It can slow down performance - in my case IN version uses index and range scan, and REGEXP version do full scan.
After examining various solutions in different forums and not finding a good solution, I feel the below hack I came up with, is the easiest to follow and code:
Example: Suppose you have multiple parameters to pass in the 'IN' clause. Just put a dummy String inside the 'IN' clause, say, "PARAM" do denote the list of parameters that will be coming in the place of this dummy String.
select * from TABLE_A where ATTR IN (PARAM);
You can collect all the parameters into a single String variable in your Java code. This can be done as follows:
String param1 = "X";
String param2 = "Y";
String param1 = param1.append(",").append(param2);
You can append all your parameters separated by commas into a single String variable, 'param1', in our case.
After collecting all the parameters into a single String you can just replace the dummy text in your query, i.e., "PARAM" in this case, with the parameter String, i.e., param1. Here is what you need to do:
String query = query.replaceFirst("PARAM",param1); where we have the value of query as
query = "select * from TABLE_A where ATTR IN (PARAM)";
You can now execute your query using the executeQuery() method. Just make sure that you don't have the word "PARAM" in your query anywhere. You can use a combination of special characters and alphabets instead of the word "PARAM" in order to make sure that there is no possibility of such a word coming in the query. Hope you got the solution.
Note: Though this is not a prepared query, it does the work that I wanted my code to do.
Just for completeness and because I did not see anyone else suggest it:
Before implementing any of the complicated suggestions above consider if SQL injection is indeed a problem in your scenario.
In many cases the value provided to IN (...) is a list of ids that have been generated in a way that you can be sure that no injection is possible... (e.g. the results of a previous select some_id from some_table where some_condition.)
If that is the case you might just concatenate this value and not use the services or the prepared statement for it or use them for other parameters of this query.
query="select f1,f2 from t1 where f3=? and f2 in (" + sListOfIds + ");";
PreparedStatement doesn't provide any good way to deal with SQL IN clause. Per http://www.javaranch.com/journal/200510/Journal200510.jsp#a2 "You can't substitute things that are meant to become part of the SQL statement. This is necessary because if the SQL itself can change, the driver can't precompile the statement. It also has the nice side effect of preventing SQL injection attacks." I ended up using following approach:
String query = "SELECT my_column FROM my_table where search_column IN ($searchColumns)";
query = query.replace("$searchColumns", "'A', 'B', 'C'");
Statement stmt = connection.createStatement();
boolean hasResults = stmt.execute(query);
do {
if (hasResults)
return stmt.getResultSet();
hasResults = stmt.getMoreResults();
} while (hasResults || stmt.getUpdateCount() != -1);
OK, so I couldn't remember exactly how (or where) I did this before so I came to stack overflow to quickly find the answer. I was surprised I couldn't.
So, how I got around the IN problem a long time ago was with a statement like this:
where myColumn in ( select regexp_substr(:myList,'[^,]+', 1, level) from dual connect by regexp_substr(:myList, '[^,]+', 1, level) is not null)
set the myList parameter as a comma delimited string: A,B,C,D...
Note: You have to set the parameter twice!
This is not the ideal practice, yet it's simple and works well for me most of the time.
where ? like concat( "%|", TABLE_ID , "|%" )
Then you pass through ? the IDs in this way: |1|,|2|,|3|,...|
I have a table aps_sections with many integer fields (such as bare_width and worn_width). I also have multiple look up tables (such as aps_bare_width and aps_worn_width) which contain an ID column and a WEIGHTING column. The ID is recorded in the above columns of the aps_sections table. I need to sum the WEIGHTINGs of the columns in the aps_sections table (whereby the WEIGHTING value comes from the look up tables). I have successfully managed this using the below SELECT statement.
SELECT aps_sections.ogc_fid,
( aps_bare_width.weighting
+ aps_worn_width.weighting
+ aps_gradient.weighting
+ aps_braiding.weighting
+ aps_pigeon.weighting
+ aps_depth.weighting
+ aps_standing_water.weighting
+ aps_running_water.weighting
+ aps_roughness.weighting
+ aps_surface.weighting
+ aps_dynamic.weighting
+ aps_ex_cond.weighting
+ aps_promotion.weighting
+ aps_level_of_use.weighting) AS calc
FROM row_access.aps_sections,
row_access.aps_bare_width,
row_access.aps_worn_width,
row_access.aps_gradient,
row_access.aps_braiding,
row_access.aps_pigeon,
row_access.aps_depth,
row_access.aps_standing_water,
row_access.aps_running_water,
row_access.aps_roughness,
row_access.aps_surface,
row_access.aps_dynamic,
row_access.aps_ex_cond,
row_access.aps_promotion,
row_access.aps_level_of_use
WHERE aps_bare_width.fid = aps_sections.bare_width
AND aps_worn_width.fid = aps_sections.worn_width
AND aps_gradient.fid = aps_sections.gradient
AND aps_braiding.fid = aps_sections.braiding
AND aps_pigeon.fid = aps_sections.pigeon
AND aps_depth.fid = aps_sections.depth
AND aps_standing_water.fid = aps_sections.standing_water
AND aps_running_water.fid = aps_sections.running_water
AND aps_roughness.fid = aps_sections.roughness
AND aps_surface.fid = aps_sections.surface
AND aps_dynamic.fid = aps_sections.dynamic
AND aps_ex_cond.fid = aps_sections.ex_cond
AND aps_promotion.fid = aps_sections.promotion
AND aps_level_of_use.fid = aps_sections.level_of_use
What I now need to do is create a function that adds the calculated result to the physical_sn_priority column of the aps_sections table. My understanding so far is that my function should look similar to:
CREATE OR REPLACE FUNCTION row_access.aps_weightings()
RETURNS trigger AS
$BODY$
BEGIN
NEW.physical_sn_priority := ;
RETURN NEW;
END;
$BODY$
LANGUAGE plpgsql VOLATILE
COST 100;
ALTER FUNCTION public.update_km()
OWNER TO postgres;
But I don't know what to put after NEW.physical_sn_priority :=. I am a beginner to SQL and to PostgreSQL so I would appreciate any guidance!
While Erwin is (as always) correct that a version would be helpful, I think your answer will be simplest with the SELECT ... INTO construction for PL/pgSQL. (Not the same as SELECT INTO that works like INSERT or CREATE TABLE.)
SELECT ( aps_bare_width.weighting
+ /* obvious deletia */
+ aps_level_of_use.weighting)
INTO NEW.physical_sn_priority
FROM row_access.aps_bare_width,
/* snip */,
row_access.aps_level_of_use
WHERE aps_bare_width.fid = NEW.bare_width
AND /* snip */
aps_level_of_use.fid = NEW.level_of_use;
RETURN NEW;
According to the documentation, the INTO can appear in several other places in the line; I find this simple to understand.
[EDIT]
While this works, on reflection, I think the schema should be revised.
CREATE TYPE weighted_item_t AS ENUM ('bare_width', /* ... */, 'level_of_use');
CREATE TABLE current_weights(item_type weighted_item_t, fid int, current_weight float);
/* key and checks omitted */
/* note, if item_type can be deduced from fid, we don't even need the enum */
CREATE TABLE sections_items(section_id int /* FK into aps_sections */,
item_type weighted_item_t, fid int);
Now the queries are going to collapse into simple sums. You need to insert records into section_items before aps_sections, which can be done with deferred constraints in a transaction with or without a stored procedure, depending on how you acquire the data and how much control you have over its format. If (and this is not clear, because it won't change on updates) you want the denormalized total, you can get it with
SELECT SUM(current_weight) INTO NEW.physical_sn_priority
FROM section_items NATURAL JOIN current_weights
WHERE NEW.section_id=section_items.section_id;
This will work out much better if additional weighted characteristics are added at some future date.
Simplified test case
You should present your question with less noise. This shorter query does the job just fine:
SELECT aps_sections.ogc_fid,
( aps_bare_width.weighting
+ aps_worn_width.weighting
+ aps_gradient.weighting) AS calc
FROM row_access.aps_sections,
row_access.aps_bare_width,
row_access.aps_worn_width,
row_access.aps_gradient,
WHERE aps_bare_width.fid = aps_sections.bare_width
AND aps_worn_width.fid = aps_sections.worn_width
AND aps_gradient.fid = aps_sections.gradient;
Answer
As #Andrew already advised, the golden way would be to simplify your schema.
If, for some reason, this is not possible, here is an alternative to simplify the addition of many columns (which may or may not be NULL), create this tiny, powerful function:
CREATE OR REPLACE FUNCTION f_sum(ANYARRAY)
RETURNS numeric LANGUAGE sql AS
'SELECT sum(i)::numeric FROM unnest($1) i';
Call:
SELECT f_sum('{2,NULL,7}'::int[])
It takes a polymorphic array type and returns numeric. Works for any number type that can be summed by sum(). Cast the result if needed.
Simplifies the syntax for summing lots of columns.
NULL values won't break your calculation because the aggregate function sum() ignores those.
In a trigger function this could be used like this:
NEW.physical_sn_priority := f_sum(ARRAY [
COALESCE(physical_sn_priority, 0) -- add to original value
,(SELECT weighting FROM aps_bare_width x WHERE x.fid = NEW.bare_width)
,(SELECT weighting FROM aps_worn_width x WHERE x.fid = NEW.worn_width)
,(SELECT weighting FROM aps_gradient x WHERE x.fid = NEW.gradient)
...
])
Since all your joined tables are only good for looking up a single field, and completely independent from each other, you can just as well use individual subqueries. I also went this way, because we do not know whether any of the subqueries might return NULL, in which case your original query or Andrew's version would result in no row / no assignment.
Assignment to NEW really only makes sense in a BEFORE trigger on the table aps_sections. This code works BEFORE INSERT (where the row cannot be found in the table yet!) as well as BEFORE UPDATE. You want to use the current values from NEW, not the old row version in the table.