ON DUPLICATE KEY UPDATE

标签：sim   table   nts   sig   increase   tab   title   val   5.7   

If you specify ON DUPLICATE KEY UPDATE, and a row is inserted that would cause a duplicate value in a UNIQUE index or PRIMARY KEY, MySQL performs an UPDATE of the old row. For example, if column a is declared as UNIQUE and contains the value1, the following two statements have similar effect:

INSERT INTO table (a,b,c) VALUES (1,2,3)
  ON DUPLICATE KEY UPDATE c=c+1;

UPDATE table SET c=c+1 WHERE a=1;

(The effects are not identical for an InnoDB table where a is an auto-increment column. With an auto-increment column, an INSERT statement increases the auto-increment value but UPDATE does not.)

The ON DUPLICATE KEY UPDATE clause can contain multiple column assignments, separated by commas.

ON DUPLICATE KEY UPDATE

标签：sim   table   nts   sig   increase   tab   title   val   5.7   

原文地址：http://www.cnblogs.com/studyNT/p/6054947.html