There are many occasions when you need to find duplicate values available in a column of a MySql table. Often, you may want to count the number of duplicate values in a MySQL table. In this article, we have discussed a query where you can find duplicates, triplicates, quadruplicates (or...
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The idea is to find all the Donations records that have the same date, amt and donor as one-or-more other records -- in short, a "Find Duplicates" query. The logic of the query is to first find the primary keys ('Donation_id') of these records in a subquery, then retrieve all...
例如,在执ALTER TABLE或LOCK TABLE语句行完以前,数据表无法被其他线程打开。正尝试打开一个表。 Removing duplicates 正在执行一个SELECT DISTINCT方式的查询,但是MySQL无法在前一个阶段优化掉那些重复的记录。因此,MySQL需要再次去掉重复的记录,然后再把结果发送给客户端。 Reopen table 获得了对一个表的锁,但是必须在...
mysql> create index ind_name_stu on student(name); Query OK, 0 rows affected (0.06 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> show index from student;--可以看到,多出了关于name的索引 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---...
mysql>ALTERTABLEuserDROPINDEXidx_name,ADDINDEXidx_name_login(username,last_login); QueryOK,0rowsaffected(7.88sec) Records:0Duplicates:0Warnings:0 mysql>EXPLAINSELECT *FROMuserWHEREusername="admin1"ORDERBYlast_loginDESCG ***1.row *** id:1 select_type:SIMPLE table:user partitions:NULL type:ref...
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This article is the second in a series on how to use theinnotopMySQL and InnoDB monitor. Introduction Here’s the situation: you are trying to update a table and every time you issue the query, it hangs until it times out and tells you the lock wait timeout was exceeded. Someone has ...
(0.18 sec) mysql> ALTER TABLE b ADD FOREIGN KEY (id) REFERENCES a(id) ON UPDATE CASCADE ON DELETE CASCADE; Query OK, 0 rows affected (0.10 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> INSERT INTO a VALUES(1,'foo'); INSERT INTO b VALUES(1,'bar'); Query OK, 1 row ...
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