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UPDATE

Description

You can update the column value of a record stored in the target table to a new one by using the UPDATE statement. Specify the name of the column to update and a new value in the SET clause, and specify the condition to be used to extract the record to be updated in the WHERE Clause. You can one or more tables only with one UPDATE statement.

In case of only one table is to be updated, you can specify ORDER BY Clause or LIMIT Clause. You can also limit the number of records to be updated in the LIMIT Clause. You can use the update with the ORDER BY Clause if you want to maintain the execution order or lock order of triggers.

Syntax

<UPDATE single table>

UPDATE table_name SET column_name = {expr | DEFAULT} [, column_name = {expr | DEFAULT}...]

    [WHERE search_condition]

    [ORDER BY {col_name | expr}]

    [LIMIT row_count]

 

<UPDATE multiple tables>

UPDATE <table_specifications> SET column_name = {expr | DEFAULT} [, column_name = {expr | DEFAULT}...]

    [WHERE search_condition]

  • <table_specifications>: You can specify the statement such as FROM clause of the SELECT  statement and one or more tables can be specified.
  • column_name: Specifies the column name to be updated. Columns for one or more tables can be specified.
  • expr | DEFAULT: Specifies a new value for the column and expression or DEFAULT keyword can be specified as a value. The SELECT statement returning result record also can be specified.
  • search_condition: Update only data that meets the search_condition if conditions are specified in the WHERE Clause.
  • col_name | expr: Specifies base column to be updated.
  • row_count: Specifies the number of records to be updated after the LIMIT Clause. An integer greater than 0 can be specified.

Note In 9.0 or lower versions, only one table can be entered in <table_specifications>.

Example 1

The following example shows how to update one table.

--creating a new table having all records copied from a_tbl1

CREATE TABLE a_tbl5 AS SELECT * FROM a_tbl1;

SELECT * FROM a_tbl5 WHERE name IS NULL;

 

           id  name                  phone

=========================================================

         NULL  NULL                  '000-0000'

            4  NULL                  '000-0000'

            5  NULL                  '000-0000'

            7  NULL                  '777-7777'

 

UPDATE a_tbl5 SET name='yyy', phone='999-9999' WHERE name IS NULL LIMIT 3;

SELECT * FROM a_tbl5;

 

           id  name                  phone

=========================================================

         NULL  'yyy'                 '999-9999'

            1  'aaa'                 '000-0000'

            2  'bbb'                 '000-0000'

            3  'ccc'                 '333-3333'

            4  'yyy'                 '999-9999'

            5  'yyy'                 '999-9999'

            6  'eee'                 '000-0000'

            7  NULL                  '777-7777'

 

-- using triggers, that the order in which the rows are updated is modified by the ORDER BY clause.

 

CREATE TABLE t (i INT,d INT);

CREATE TRIGGER trigger1 BEFORE UPDATE ON t IF new.i < 10 EXECUTE PRINT 'trigger1 executed';

CREATE TRIGGER trigger2 BEFORE UPDATE ON t IF new.i > 10 EXECUTE PRINT 'trigger2 executed';

INSERT INTO t VALUES (15,1),(8,0),(11,2),(16,1), (6,0),(1311,3),(3,0);

UPDATE t  SET i = i + 1 WHERE 1 = 1;

 

trigger2 executed

trigger1 executed

trigger2 executed

trigger2 executed

trigger1 executed

trigger2 executed

trigger1 executed

 

TRUNCATE TABLE t;

INSERT INTO t VALUES (15,1),(8,0),(11,2),(16,1), (6,0),(1311,3),(3,0);

UPDATE t SET i = i + 1 WHERE 1 = 1  ORDER BY i;

 

trigger1 executed

trigger1 executed

trigger1 executed

trigger2 executed

trigger2 executed

trigger2 executed

trigger2 executed

Example 2

The following example shows how to update multiple tables after joining them.

CREATE TABLE a_tbl(id INT PRIMARY KEY, charge DOUBLE);

CREATE TABLE b_tbl(rate_id INT, rate DOUBLE);

INSERT INTO a_tbl VALUES (1, 100.0), (2, 1000.0), (3, 10000.0);

INSERT INTO b_tbl VALUES (1, 0.1), (2, 0.0), (3, 0.2), (3, 0.5);

 

UPDATE

 a_tbl INNER JOIN b_tbl ON a_tbl.id=b_tbl.rate_id

SET

  a_tbl.charge = a_tbl.charge * (1 + b_tbl.rate)

WHERE a_tbl.charge > 900.0;

For the a_tbl table and the b_tbl table, which join the UPDATE statement, when the number of rows of a_tbl which joins one row of b_tbl is two or more and the column to be updated is included in a_tbl, update is executed by using the value of the row detected first among the rows of b_tbl.

In the above example, when the number of rows with id=5, the JOIN condition column, is one in a_tbl and two in b_tbl, a_tbl.charge, the update target column in the row with a_tbl.id=5, uses the value of rate of the first row in b_tbl only.