I am a novice Oracle user. I wanted to update a boolean field in my table for one of the record. Which one of these statements is correct ?
update MyTable set myBooleanColumn = 1 where UserId= 'xx12345';
or
update MyTable set myBooleanColumn = '1' where UserId= 'xx12345';
any help is greatly appreciated!! thanks !
It depends on how the field is defined.
If its defined as a CHAR(1) field, then you can store 'Y'/'N' or 'T'/'F' in it. To update the field, you'd use the quotes as it would be a string literal.
UPDATE TestTable set myCharBooleanColumn = 'Y';
If the field is defined as NUMERIC, then the convention is 0=false and 1 or -1 is true (I've seen both).
UPDATE TestTable set myNumericBooleanColumn = 1;
Many people will advocate the CHAR(1) approach, but in the real world - you see both. It depends on how the boolean is implemented.
You can read more in Oracle's docs on Datatypes
http://docs.oracle.com/cd/B28359_01/server.111/b28318/datatype.htm
There is no such thing as a Boolean field in Oracle so your field is either a numeric field or a character field. If it's a numeric field you don't need to quote the number; if it's a character field you should quote the string.
You can find out the type of the column by querying USER_TAB_COLUMNS:
select *
from user_tab_columns
where table_name = 'MYTABLE'
and column_name = 'MYBOOLEANCOLUMN'
or by describing the table.
There is nothing as Boolean field in Oracle.
The best what you can do is to create the table like this:-
create table ABC(bool char(1) check (bool in ('N','Y'));
Then simple update like
UPDATE ABC set bool = 'Y';
WHY TAKING CHAR?
There is no support for BOOLEAN, BIT, or TINYINT data types so char would be the best as it takes 1 byte
Related
I have a SQL Server database and I've changed my mind and instead of a column in my table being set as an int, I want to change it to a varchar. So I changed the type to varchar(8), and saved my changes in SQL Server Management Studio tool (V17.0).
It looks like the tool converted the int values to varchars when I saved the changes. I want to change the value of '1' to 'External', '2' to 'SPTR' and '3' to 'Other'. I was going to do one value at a time.
This is the simple SQL statement I tried:
UPDATE mytable
SET mycolumn = 'External'
WHERE mycolumn = '1'
The error message I get from SSMS is
Conversion failed when converting the varchar value 'External' to data type int"
It's as if the database thinks the type is int, but it's not, it's varchar(8).
Sounds like you really haven't changed the data type. This should resolve the problem.
ALTER TABLE mytable ALTER COLUMN mycolumn varchar(8);
GO
UPDATE mytable
SET mycolumn = CASE mycolumn WHEN '1' THEN 'External'
WHEN '2' THEN 'SPTR'
ELSE 'OTHER'
END;
Note, as well, you can update every value at the same time by using a CASE expression. Likely far easier than 3 UPDATE statements.
ALTER TABLE mytable ALTER COLUMN mycolumn varchar(50);
SELECT DATALENGTH ('External')
returns 8
As long as I know varchar does not use all 50 bytes, it only uses 8 in your case to store "External" field, why don't you try to change table size.
If you have changed mycolumn to a string, then the following should work:
UPDATE mytable
SET mycolumn = 'External'
WHERE mycolumn = '1';
If you are getting a type conversion error, then I assume you have a trigger on the table that is causing the problem. You might be wrong in saying that the type has changed. But even if you are correct, a trigger could still generate this issue.
Is it possible to copy data from column A to column B for all records in a table in SQL?
How about this
UPDATE table SET columnB = columnA;
This will update every row.
UPDATE table_name SET
destination_column_name=orig_column_name
WHERE condition_if_necessary
This will update all the rows in that columns if safe mode is not enabled.
UPDATE table SET columnB = columnA;
If safe mode is enabled then you will need to use a where clause.
I use primary key as greater than 0 basically all will be updated
UPDATE table SET columnB = columnA where table.column>0;
If you want to copy a column to another column with a different data type in PostgresSQL, you must cast/convert to the data type first, otherwise it will return
Query 1 ERROR: ERROR: column "test_date" is of type timestamp without
time zone but expression is of type character varying LINE 1: update
table_name set test_date = date_string_col
^ HINT: You will need to rewrite or cast the expression.
An example of converting varchar to timestamp:
update table_name set timestamp_col = date_string_col::TIMESTAMP;
An example of converting varchar to int:
update table_name set int_column = string_col::INTEGER;
but any column type(except file or the similar) can be copied to string(character varying) without cast the type.
I want to declare a variable in SQLite and use it in insert operation.
Like in MS SQL:
declare #name as varchar(10)
set name = 'name'
select * from table where name = #name
For example, I will need to get last_insert_row and use it in insert.
I have found something about binding but I didn't really fully understood it.
SQLite doesn't support native variable syntax, but you can achieve virtually the same using an in-memory temp table.
I've used the below approach for large projects and works like a charm.
/* Create in-memory temp table for variables */
BEGIN;
PRAGMA temp_store = 2; /* 2 means use in-memory */
CREATE TEMP TABLE _Variables(Name TEXT PRIMARY KEY, RealValue REAL, IntegerValue INTEGER, BlobValue BLOB, TextValue TEXT);
/* Declaring a variable */
INSERT INTO _Variables (Name) VALUES ('VariableName');
/* Assigning a variable (pick the right storage class) */
UPDATE _Variables SET IntegerValue = ... WHERE Name = 'VariableName';
/* Getting variable value (use within expression) */
... (SELECT coalesce(RealValue, IntegerValue, BlobValue, TextValue) FROM _Variables WHERE Name = 'VariableName' LIMIT 1) ...
DROP TABLE _Variables;
END;
For a read-only variable (that is, a constant value set once and used anywhere in the query), use a Common Table Expression (CTE).
WITH const AS (SELECT 'name' AS name, 10 AS more)
SELECT table.cost, (table.cost + const.more) AS newCost
FROM table, const
WHERE table.name = const.name
SQLite WITH clause
Herman's solution works, but it can be simplified because Sqlite allows to store any value type on any field.
Here is a simpler version that uses one Value field declared as TEXT to store any value:
CREATE TEMP TABLE IF NOT EXISTS Variables (Name TEXT PRIMARY KEY, Value TEXT);
INSERT OR REPLACE INTO Variables VALUES ('VarStr', 'Val1');
INSERT OR REPLACE INTO Variables VALUES ('VarInt', 123);
INSERT OR REPLACE INTO Variables VALUES ('VarBlob', x'12345678');
SELECT Value
FROM Variables
WHERE Name = 'VarStr'
UNION ALL
SELECT Value
FROM Variables
WHERE Name = 'VarInt'
UNION ALL
SELECT Value
FROM Variables
WHERE Name = 'VarBlob';
Herman's solution worked for me, but the ... had me mixed up for a bit. I'm including the demo I worked up based on his answer. The additional features in my answer include foreign key support, auto incrementing keys, and use of the last_insert_rowid() function to get the last auto generated key in a transaction.
My need for this information came up when I hit a transaction that required three foreign keys but I could only get the last one with last_insert_rowid().
PRAGMA foreign_keys = ON; -- sqlite foreign key support is off by default
PRAGMA temp_store = 2; -- store temp table in memory, not on disk
CREATE TABLE Foo(
Thing1 INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL
);
CREATE TABLE Bar(
Thing2 INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
FOREIGN KEY(Thing2) REFERENCES Foo(Thing1)
);
BEGIN TRANSACTION;
CREATE TEMP TABLE _Variables(Key TEXT, Value INTEGER);
INSERT INTO Foo(Thing1)
VALUES(2);
INSERT INTO _Variables(Key, Value)
VALUES('FooThing', last_insert_rowid());
INSERT INTO Bar(Thing2)
VALUES((SELECT Value FROM _Variables WHERE Key = 'FooThing'));
DROP TABLE _Variables;
END TRANSACTION;
To use the one from denverCR in your example:
WITH tblCTE AS (SELECT "Joe" AS namevar)
SELECT * FROM table, tblCTE
WHERE name = namevar
As a beginner I found other answers too difficult to understand, hope this works
Creating "VARIABLE" for use in SQLite SELECT (and some other) statements
CREATE TEMP TABLE IF NOT EXISTS variable AS SELECT '2002' AS _year; --creating the "variable" named "_year" with value "2002"
UPDATE variable SET _year = '2021'; --changing the variable named "_year" assigning "new" value "2021"
SELECT _year FROM variable; --viewing the variable
SELECT 'TEST', (SELECT _year FROM variable) AS _year; --using the variable
SELECT taxyr FROM owndat WHERE taxyr = (SELECT _year FROM variable); --another example of using the variable
SELECT DISTINCT taxyr FROM owndat WHERE taxyr IN ('2022',(SELECT _year FROM variable)); --another example of using the variable
DROP TABLE IF EXISTS variable; --releasing the "variable" if needed to be released
After reading all the answers I prefer something like this:
select *
from table, (select 'name' as name) const
where table.name = const.name
Try using Binding Values. You cannot use variables as you do in T-SQL but you can use "parameters". I hope the following link is usefull.Binding Values
I found one solution for assign variables to COLUMN or TABLE:
conn = sqlite3.connect('database.db')
cursor=conn.cursor()
z="Cash_payers" # bring results from Table 1 , Column: Customers and COLUMN
# which are pays cash
sorgu_y= Customers #Column name
query1="SELECT * FROM Table_1 WHERE " +sorgu_y+ " LIKE ? "
print (query1)
query=(query1)
cursor.execute(query,(z,))
Don't forget input one space between the WHERE and double quotes
and between the double quotes and LIKE
I am using Oracle DB. At the database level, when you set a column value to either NULL or '' (empty string), the fetched value is NULL in both cases. Is it possible to store '' (empty string) as a non NULL value in the database?
I execute this
UPDATE contacts SET last_name = '' WHERE id = '1001';
commit;
SELECT last_name, ID FROM contacts WHERE id ='1001';
LAST_NAME ID
------------ ------
null 1001
Is it possible to store the last_name as a non-NULL empty string ('')?
The only way to do this in oracle is with some kind of auxiliary flag field, that when set is supposed to represent the fact that the value should be an empty string.
As far as i know Oracle does not distinguish between '' and NULL, see here.
Oracle has a well know behavior that it silently converts "" to NULL on INSERT and UPDATE statements.
You have to deal with this in your code to prevent this behavior by converting NULL to "" when you read the columns back in and just do not use null in your program to begin with.
A long time since I used Oracle, but I believe we used to use a single space ' ' to represent an empty string, then trim it after reading.
If you use a VARCHAR2 data type then NULL and '' are identical and you cannot distinguish between them; so, as mentioned in other answers, you would either need to:
Have an additional column that contains a flag that distinguishes between non-NULL and NULL values so that if then flag states it is non-NULL and it contains a NULL then you know it is an empty string; or
Use an alternate representation, such as a single space character, for an empty string. This would then mean that you cannot store a string with that alternate representation; however, if trailing white-space was syntactically invalid for the strings you are storing then using a single space character to represent an empty string would be fine.
If you are using a CLOB data type then you CAN store an empty string using the EMPTY_CLOB() function:
CREATE TABLE table_name (value CLOB);
INSERT INTO table_name (value) VALUES (NULL);
INSERT INTO table_name (value) VALUES (EMPTY_CLOB());
INSERT INTO table_name (value) VALUES ('A');
Then:
SELECT value, LENGTH(value) FROM table_name;
Outputs:
VALUE
LENGTH(VALUE)
null
null
0
A
1
db<>fiddle here
How do I clear the value from a cell and make it NULL?
I think Zack properly answered the question but just to cover all the bases:
Update myTable set MyColumn = NULL
This would set the entire column to null as the Question Title asks.
To set a specific row on a specific column to null use:
Update myTable set MyColumn = NULL where Field = Condition.
This would set a specific cell to null as the inner question asks.
If you've opened a table and you want to clear an existing value to NULL, click on the value, and press Ctrl+0.
If you are using the table interface you can type in NULL (all caps)
otherwise you can run an update statement where you could:
Update table set ColumnName = NULL where [Filter for record here]
Use This:
Update Table Set Column = CAST(NULL As Column Type) where Condition
Like This:
Update News Set Title = CAST(NULL As nvarchar(100)) Where ID = 50
Ctrl+0 or empty the value and hit enter.
Just as a little extension to Jeff Martin's and Zack Peterson's solution.
If you still want to set several values from the columns to null you can simply set the query to
UPDATE myTable SET MyColumn1 = NULL, MyColumn2 = NULL, MyColumn3 = NULL, ...
CTRL+0 doesn't seem to work when connected to an Azure DB.
However, to create an empty string, you can always just hit 'anykey then delete' inside a cell.