Update (SQL)
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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 condition.
The UPDATE statement has the following form:
UPDATEtable_nameSETcolumn_name = value [, column_name = value ...] [WHEREcondition];
For the UPDATE to be successful, the user must have data manipulation privileges (UPDATE privilege) over the table or column, the updated value must not conflict with all the applicable constraints (such as primary keys, unique indexes, CHECK constraints, and NOT NULL constraints).
[edit] Examples
Set the value of column C1 in table T column to 1, only if in that row the value of C2 is "a".
UPDATE T SET C1 = 1 WHERE C2 = 'a';
Increase value of column C1 by 1 if C2 is "a".
UPDATE T SET C1 = C1 + 1 WHERE C2 = 'a';
Prepend column C1 with the string "text" if C2 is "a".
UPDATE T SET C1 = CONCAT( 'text' , C1 ) WHERE C2 = 'a';
Mass update example: Set the value of column C1 in table T1 to 2, only if the value of column C2 is found in the sub list of values in column C3 in table T2 having the column C4 equal to 0.
UPDATE T1
SET
C1 = 2
WHERE C2 in (SELECT C3
FROM T2
WHERE C4 = 0);
You may also update multiple fields in a single update statement:
UPDATE T SET C1 = 1, C2 = 2;
Complex conditions are also possible:
UPDATE T SET A = 1 WHERE C1 = 1 AND C2 = 2;
Conditions can be imposed even on fields coming from a JOIN operation:
UPDATE T1 INNER JOIN T2 ON T1.key = T2.key SET C1 = 1 WHERE T1.C2 = 2, T2.C3 = 3
