config root man

#
# TRUNCATE TABLE
#
# Truncating is disallowed for parent tables unless such table
# participates in self-referencing foreign keys only.
#
CREATE TABLE t1 (pk INT PRIMARY KEY) ENGINE=INNODB;
CREATE TABLE t2 (fk INT NOT NULL, FOREIGN KEY (fk) REFERENCES t1 (pk)) ENGINE=INNODB;
TRUNCATE TABLE t1;
ERROR 42000: Cannot truncate a table referenced in a foreign key constraint (`test`.`t2`, CONSTRAINT `t2_ibfk_1` FOREIGN KEY (`fk`) REFERENCES `test`.`t1` (`pk`))
# Truncation of child should succeed.
TRUNCATE TABLE t2;
DROP TABLE t2;
DROP TABLE t1;
CREATE TABLE t1 (pk INT PRIMARY KEY, fk INT,
FOREIGN KEY (fk) REFERENCES t1 (pk)) ENGINE=INNODB;
# Truncation of self-referencing table should succeed.
TRUNCATE TABLE t1;
DROP TABLE t1;
#
# Also, truncating such tables is allowed if foreign key
# checks are disabled.
#
SET @old_foreign_key_checks = @@SESSION.foreign_key_checks;
CREATE TABLE t1 (pk INT PRIMARY KEY) ENGINE=INNODB;
CREATE TABLE t2 (fk INT NOT NULL, FOREIGN KEY (fk) REFERENCES t1 (pk)) ENGINE=INNODB;
CREATE TABLE t3 (pk INT PRIMARY KEY, fk INT,
FOREIGN KEY (fk) REFERENCES t1 (pk)) ENGINE=INNODB;
SET @@SESSION.foreign_key_checks = 0;
TRUNCATE TABLE t1;
TRUNCATE TABLE t2;
TRUNCATE TABLE t3;
SET @@SESSION.foreign_key_checks = 1;
TRUNCATE TABLE t1;
ERROR 42000: Cannot truncate a table referenced in a foreign key constraint (`test`.`t2`, CONSTRAINT `t2_ibfk_1` FOREIGN KEY (`fk`) REFERENCES `test`.`t1` (`pk`))
TRUNCATE TABLE t2;
TRUNCATE TABLE t3;
LOCK TABLES t1 WRITE;
SET @@SESSION.foreign_key_checks = 0;
TRUNCATE TABLE t1;
SET @@SESSION.foreign_key_checks = 1;
TRUNCATE TABLE t1;
ERROR 42000: Cannot truncate a table referenced in a foreign key constraint (`test`.`t2`, CONSTRAINT `t2_ibfk_1` FOREIGN KEY (`fk`) REFERENCES `test`.`t1` (`pk`))
UNLOCK TABLES;
DROP TABLE t3,t2,t1;
SET @@SESSION.foreign_key_checks = @old_foreign_key_checks;
#
# Test that TRUNCATE resets auto-increment.
#
CREATE TABLE t1 (a INT PRIMARY KEY NOT NULL AUTO_INCREMENT);
INSERT INTO t1 VALUES (NULL), (NULL);
SELECT AUTO_INCREMENT FROM INFORMATION_SCHEMA.TABLES WHERE table_name = 't1';
AUTO_INCREMENT
3
SELECT * FROM t1 ORDER BY a;
a
1
2
TRUNCATE TABLE t1;
SELECT AUTO_INCREMENT FROM INFORMATION_SCHEMA.TABLES WHERE table_name = 't1';
AUTO_INCREMENT
1
INSERT INTO t1 VALUES (NULL), (NULL);
SELECT * FROM t1 ORDER BY a;
a
1
2
DROP TABLE t1;