An SQL UPDATE statement changes the data of one or more records in a table. Either all the rows can be updated, or a subset may be chosen using a <code>WHERE</code> condition. If a condition is not used, then every row of the value is updated.
The <code>UPDATE</code> statement has the following form:
Because of this indeterminacy, referencing other tables only within sub-selects is safer, though often harder to read and slower than using a join.
MySQL does not conform to the ANSI standard.
Examples
Set the value of column C1 in table T to 1, only in those rows where the value of column C2 is "a".
<syntaxhighlight lang="sql">
UPDATE T
SET C1 = 1
WHERE C2 = 'a'
</syntaxhighlight>
In table T, set the value of column C1 to 9 and the value of C3 to 4 for all rows for which the value of column C2 is "a".
<syntaxhighlight lang="sql">
UPDATE T
SET C1 = 9,
C3 = 4
WHERE C2 = 'a'</syntaxhighlight>
Increase value of column C1 by 1 if the value in column C2 is "a".
<syntaxhighlight lang="sql">
UPDATE T
SET C1 = C1 + 1
WHERE C2 = 'a'</syntaxhighlight>
Prepend the value in column C1 with the string "text" if the value in column C2 is "a".
<syntaxhighlight lang="sql">
UPDATE T
SET C1 = 'text' || C1
WHERE C2 = 'a'</syntaxhighlight>
Set the value of column C1 in table T1 to 2, only if the value of column C2 is found in the sublist of values in column C3 in table T2 having the column C4 equal to 0.
<syntaxhighlight lang="sql">
UPDATE T1
SET C1 = 2
WHERE C2 IN ( SELECT C3
FROM T2
WHERE C4 = 0)
</syntaxhighlight>
One may also update multiple columns in a single update statement:
<syntaxhighlight lang="sql">
UPDATE T
SET C1 = 1,
C2 = 2</syntaxhighlight>
Complex conditions and JOINs are also possible:
<syntaxhighlight lang="sql">
UPDATE T
SET A = 1
WHERE C1 = 1
AND C2 = 2</syntaxhighlight>
Some databases allow the non-standard use of the FROM clause:
<syntaxhighlight lang="sql">
UPDATE a
SET a.[updated_column] = updatevalue
FROM articles a
JOIN classification c
ON a.articleID = c.articleID
WHERE c.classID = 1
</syntaxhighlight>
Or on Oracle systems (assuming there is an index on classification.articleID):
<syntaxhighlight lang="sql">
UPDATE
(
SELECT *
FROM articles
JOIN classification
ON articles.articleID = classification.articleID
WHERE classification.classID = 1
)
SET [updated_column] = updatevalue
</syntaxhighlight>
With long name of table:
<syntaxhighlight lang="sql">
UPDATE MyMainTable AS a
SET a.LName = Smith
WHERE a.PeopleID = 1235
</syntaxhighlight>
Potential issues
- See Halloween Problem. It is possible for certain kinds of <code>UPDATE</code> statements to become an infinite loop when the <code>WHERE</code> clause and one or more <code>SET</code> clauses may utilize an intertwined index.