I have a scenario where I would like to update multiple fields in multiple Tables using just one instuction. I need a Syntax to perform such opperations on multiple Databases (Oracle and MSSQL).
At the moment I am stuck at the following statement from MSSQL:
update table1
set table1.value = 'foo'
from table1 t1 join table2 t2 on t1.id = t2.tab1_id
where t1.id = 1234
I would like to update a field in t2 aswell in the same statement.
Further I would like to perform the same Update(s) on Oracle.
EDIT:Seems like I can not update multiple Tables in just one statement. Is there a syntax that works for Oracle and MSSql when updating using a Join?
Regards
Seems like I can not update multiple
Tables in just one statement.
Is there a syntax that works for
Oracle and MSSql when updating using a
Join?
I assume when you re-posed the question you want syntax that will work on both Oracle and SQL Server even though it will inevitably affect only one table.
Entry level SQL-92 Standard code is supported by both platforms, therefore the following 'scalar subqueries' SQL-92 code should work:
UPDATE table1
SET my_value = (
SELECT t2.tab1_id
FROM table2 AS t2
WHERE t2.tab1_id = table1.id
)
WHERE id = 1234
AND EXISTS (
SELECT *
FROM table2 AS t2
WHERE t2.tab1_id = table1.id
);
Note that while using the correlation name t1 for Ttble1 is valid syntax according to the SQL-92 Standard this will materialize a table and the UPDATE will then target the materialized table 't1' and leave your base table 'table1` unaffected, which I assume is not the desired affect. While I'm fairly sure both Oracle and SQL Server are non-compliant is this regard and that in practise would work as expected, there's no harm in being ultra cautious and sticking to the SQL-92 syntax by fully qualifying the target table.
Folk tend not to like the 'repeated' code in the above subqueries (even though the optimizer should be smart enough to evaluate it only once).
More recent versions of Oracle and SQL Server support both support Standard SQL:2003 MERGE syntax, would may be able to use something close to this:
MERGE INTO table1
USING (
SELECT t2.tab1_id
FROM table2 AS t2
) AS source
ON id = source.tab1_id
AND id = 1234
WHEN MATCHED THEN
UPDATE
SET my_value = source.tab1_id;
I just noticed your example is even simpler than I first thought and merely requires a simple subquery that should run on most SQL products e.g.
UPDATE table1
SET my_value = 'foo'
WHERE EXISTS (
SELECT *
FROM table2 AS t2
WHERE t2.tab1_id = table1.id
);
on Oracle, you can update only one table , but you could think of using a trigger .
Related
Trying to do this:
UPDATE table1 t1
SET cost = t2.price
FROM table2 t2
WHERE t1.item_id = t2.item_id
It's working on PostgreSQL but not working on HSQLDB.
How to fix this script to support working both on PostgreSQL and HSQLDB?
The UPDATE ... FROM syntax is non-standard. This is Standard SQL and works in HSQLDB (and apparently in PostgreSQL). I am really surprised that PostgreSQL 9.4 syntax documentation does not mention this syntax which has been in the Standard since 1992.
UPDATE table1 t1
SET cost = (SELCT t2.price
FROM table2 t2
WHERE t1.item_id = t2.item_id)
HSQLDB does not support UPDATE ... FROM statements. On HSQLDB use the MERGE statement instead. Out of my head, hoping this does not contain syntax errors:
MERGE INTO table1 USING table2 ON table1.item_id = table2.item_id
WHEN MATCHED THEN UPDATE SET table1.cost = table2.price
Unfortunately, as of today postgres does not seem to support the MERGE statement, but only the similar UPSERT.
Strangely, it seems that the EXISTS clause is not supported by DBISAM's sql engine, as it's always resulting in an SQL error. The following is a sample where EXISTS is being used. Am i missing anything here?
update Table1 set HASXACTION = False
WHERE EXISTS (SELECT SERIALID
From Table2
LEFT JOIN Table1 ON (Table2 .AUXILACT = Table1 .CODE)
AND (Table2 .CHARTACT = Table1 .CHARTACT) )
Never mind people, i just learned that DBISAM does not support EXISTS operator for specifying sub-select predicates in WHERE clauses. It's documented within DBISAM's help file(screenshot attached).
I presume that you don't really want the join in the subquery. You probably intend a correlated subquery:
UPDATE Table1
SET HASXACTION = False
WHERE EXISTS (SELECT SERIALID
FROM Table2
WHERE Table2.AUXILACT = Table1.CODE AND Table2.CHARTACT = Table1.CHARTACT
);
This should also fix the problem you are having, which is the reference to Table1 both in the update clause and the subquery. (This is a MySQL limitation.)
EDIT:
I cannot find any reference to EXISTS (or even subqueries) for dbisam. But, you can do updates with joins, so this should be equivalent:
UPDATE Table1
SET HASXACTION = False
FROM Table1 JOIN
Table2
ON Table2.AUXILACT = Table1.CODE AND Table2.CHARTACT = Table1.CHARTACT;
As you've already found, you can do it with the IN. However, there is a limitation that IN can only work with one field. So you can get around it by concatenating two fields to make expressions that fit the criteria. One for the inner, and one for the outer.
update Table1 set HASXACTION = False
WHERE Code+'.'+CHARTACT IN
(
SELECT AUXILACT+'.'+CHARTACT From Table2
)
I've got an Access application with an update query with the following syntax:
UPDATE TABLE1, TABLE2 SET
TABLE2.VALUE1 = TABLE1.VALUE1,
TABLE2.VALUE2 = TABLE1.VALUE2,
TABLE2.VALUE3 = TABLE1.VALUE3,
TABLE2.VALUE4 = TABLE1.VALUE4
The query is working but I do not understand what's going on here.
I'm trying to convert this query to SQL Server.
Can somebody please explain what this query does? My guess is that it's a special Access syntax.
Thanks,
Sven
It uses the older implicit JOIN syntax, although SQL Server should understand that syntax too.
It's INNER JOINing table1 and table2, then moving the values from table1 to table2. Because of the lack of JOIN conditions, if table1 has more than 1 row it may have unpredictable results.
Essentially it is:
UPDATE Table1 INNER JOIN Table2 <<ON Missing Conditions Here>>
SET Table2.Value1 = Table1.Value1
Table2.Value2 = Table1.Value2
Table2.Value3 = Table1.Value3
Table2.Value4 = Table1.Value4
You can convert this to SQL Server with something like this:
UPDATE Table2
SET Table2.Value1 = Table1.Value1
Table2.Value2 = Table1.Value2
Table2.Value3 = Table1.Value3
Table2.Value4 = Table1.Value4
FROM Table1 INNER JOIN Table2 <<ON Missing Conditions Here>>
Every field from TABLE2 will override corresponded field from TABLE1 with records from TABLE1 one by one. Result will be TABLE2 with all replaced records by last row from TABLE1. If TABLE1 has no records - no changes happens.
Sorry for my english.
And... it is SQL.
Try to avoid the "UPDATE with join" syntax in SQL Server. It is completely non-standard SQL but more seriously it gives unpredictable results without any error or warning if the joining criteria is not correct. Use the MERGE statement instead or use the standard version of the UPDATE statement (with a subquery) if you can.
I've added a field to a MySQL table. I need to populate the new column with the value from another table. Here is the query that I'd like to run:
UPDATE table1 t1
SET t1.user_id =
(
SELECT t2.user_id
FROM table2 t2
WHERE t2.usr_id = t1.usr_id
)
I ran that query locally on 239K rows and it took about 10 minutes. Before I do that on the live environment I wanted to ask if what I am doing looks ok i.e. does 10 minutes sound reasonable. Or should I do it another way, a php loop? a better query?
Use an UPDATE JOIN! This will provide you a native inner join to update from, rather than run the subquery for every bloody row. It tends to be much faster.
update table1 t1
inner join table2 t2 on
t1.usr_id = t2.usr_id
set t1.user_id = t2.user_id
Ensure that you have an index on each of the usr_id columns, too. That will speed things up quite a bit.
If you have some rows that don't match up, and you want to set t1.user_id = null, you will need to do a left join in lieu of an inner join. If the column is null already, and you're just looking to update it to the values in t2, use an inner join, since it's faster.
I should make mention, for posterity, that this is MySQL syntax only. The other RDBMS's have different ways of doing an update join.
There are two rather important pieces of information missing:
What type of tables are they?
What indexes exist on them?
If table2 has an index that contains user_id and usr_id as the first two columns and table1 is indexed on user_id, it shouldn't be that bad.
You don't have an index on t2.usr_id.
Create this index and run your query again, or a multiple-table UPDATE proposed by #Eric (with LEFT JOIN, of course).
Note that MySQL lacks other JOIN methods than NESTED LOOPS, so it's index that matters, not the UPDATE syntax.
However, the multiple table UPDATE is more readable.
I need to perform a query like this:
SELECT *,
(SELECT Table1.Column
FROM Table1
INNER JOIN Table2 ON Table1.Table2Id = Table2.Id
) as tmp
FROM Table2 WHERE tmp = 1
I know I can take a workaround but I would like to know if this syntax is possible as it is (I think) in Mysql.
The query you posted won't work on sql server, because the sub query in your select clause could possibly return more than one row. I don't know how MySQL will treat it, but from what I'm reading MySQL will also yield an error if the sub query returns any duplicates. I do know that SQL Server won't even compile it.
The difference is that MySQL will at least attempt to run the query and if you're very lucky (Table2Id is unique in Table1) it will succeed. More probably is will return an error. SQL Server won't try to run it at all.
Here is a query that should run on either system, and won't cause an error if Table2Id is not unique in Table1. It will return "duplicate" rows in that case, where the only difference is the source of the Table1.Column value:
SELECT Table2.*, Table1.Column AS tmp
FROM Table1
INNER JOIN Table2 ON Table1.Table2Id = Table2.Id
WHERE Table1.Column = 1
Perhaps if you shared what you were trying to accomplish we could help you write a query that does it.
SELECT *
FROM (
SELECT t.*,
(
SELECT Table1.Column
FROM Table1
INNER JOIN
Table2
ON Table1.Table2Id = Table2.Id
) as tmp
FROM Table2 t
) q
WHERE tmp = 1
This is valid syntax, but it will fail (both in MySQL and in SQL Server) if the subquery returns more than 1 row
What exactly are you trying to do?
Please provide some sample data and desired resultset.
I agree with Joel's solution but I want to discuss why your query would be a bad idea to use (even though the syntax is essentially valid). This is a correlated subquery. The first issue with these is that they don't work if the subquery could possibly return more than one value for a record. The second and more critical problem (in my mind) is that they must work row by row rather than on the set of data. This means they will virtually always affect performance. So correlated subqueries should almost never be used in a production system. In this simple case, the join Joel showed is the correct solution.
If the subquery is more complicated, you may want to turn it into a derived table instead (this also fixes the more than one value associated to a record problem). While a derived table looks a lot like a correlated subquery to the uninitated, it does not perform the same way because it acts on the set of data rather than row-by row and thus will often be significantly faster. You are essentially making the query a table in the join.
Below is an example of your query re-written as a derived table. (Of course in production code you would not use select * either especially in a join, spell out the fields you need)
SELECT *
FROM Table2 t2
JOIN
(SELECT Table1.[Column], Table1.Table2Id as tmp
FROM Table1
INNER JOIN Table2 ON Table1.Table2Id = Table2.Id ) as t
ON t.Table2Id = Table2.Id
WHERE tmp = 1
You've already got a variety of answers, some of them more useful than others. But to answer your question directly:
No, SQL Server will not allow you to reference the column alias (defined in the select list) in the predicate (the WHERE clause). I think that is sufficient to answer the question you asked.
Additional details:
(this discussion goes beyond the original question you asked.)
As you noted, there are several workarounds available.
Most problematic with the query you posted (as others have already pointed out) is that we aren't guaranteed that the subquery in the SELECT list returns only one row. If it does return more than one row, SQL Server will throw a "too many rows" exception:
Subquery returned more than 1 value.
This is not permitted when the subquery
follows =, !=, , >= or when the
subquery is used as an expression.
For the following discussion, I'm going to assume that issue is already sufficiently addressed.
Sometimes, the easiest way to make the alias available in the predicate is to use an inline view.
SELECT v.*
FROM ( SELECT *
, (SELECT Table1.Column
FROM Table1
JOIN Table2 ON Table1.Table2Id = Table2.Id
WHERE Table1.Column = 1
) as tmp
FROM Table2
) v
WHERE v.tmp = 1
Note that SQL Server won't push the predicate for the outer query (WHERE v.tmp = 1) into the subquery in the inline view. So you need to push that in yourself, by including the WHERE Table1.Column = 1 predicate in the subquery, particularly if you're depending on that to make the subquery return only one value.
That's just one approach to working around the problem, there are others. I suspect that query plan for this SQL Server query is not going to be optimal, for performance, you probably want to go with a JOIN or an EXISTS predicate.
NOTE: I'm not an expert on using MySQL. I'm not all that familiar with MySQL support for subqueries. I do know (from painful experience) that subqueries weren't supported in MySQL 3.23, which made migrating an application from Oracle 8 to MySQL 3.23 particularly painful.
Oh and btw... of no interest to anyone in particular, the Teradata DBMS engine DOES have an extension that allows for the NAMED keyword in place of the AS keyword, and a NAMED expression CAN be referenced elsewhere in the QUERY, including the WHERE clause, the GROUP BY clause and the ORDER BY clause. Shuh-weeeet
That kind of syntax is basically valid (you need to move the where tmp=... to on outer "select * from (....)", though), although it's ambiguous since you have two sets named "Table2"- you should probably define aliases on at least one of your usages of that table to clear up the ambiguity.
Unless you intended that to return a column from table1 corresponding to columns in table2 ... in which case you might have wanted to simply join the tables?