With Duplicates as (select distinct a.custid as Customer_ID from customers2 a join customers2 b on a.custid <> b.custid and a.CustName = b.CustName and a.CustCity = b.CustCity and a.Passport_Number = b.Passport_
Write a SQL query to delete all duplicate email entries in a table namedPerson, keeping only unique emails based on itssmallestId. +---+---+ | Id | Email | +---+---+ | 1 | john@example.com | | 2 | bob@example.com | | 3 | john@example.com | +---+---+ Id is the ...
first_level=true) at /home/Code/GitHub/stonedb/sql/sql_parse.cc:3645#6 0x00000000023d175d in mysql_parse(thd=0x7fdcec000bc0,parser_state=0x7fe0c81cae70) at /home/Code/GitHub/stonedb/sql/sql_parse.cc:5655#7 0x00000000023c68b8 in dispatch_command(thd=0x7fdcec000bc0,com_dat...
关闭后上面的sql就变成先扫描外部的t_table_1,然后再逐行去匹配子查询了,假设t_table_1的数据量非常大,那全表扫描时间就会很长,我们可以通过optimizer_trace证明一下。optimizer_trace是mysql一个跟踪功能,可以跟踪优化器做的各种决策,包括sql改写,成本计算,索引选择详细过程,并将跟踪结果记录到INFORMATION_SCHEMA.OPTI...
However, a single SQL query can do the whole process, including prioritization of rows and the number of duplicates to keep. Usage MySQL WITH duplicates AS ( SELECT id, ROW_NUMBER() OVER( PARTITION BY firstname, lastname, email ORDER BY age DESC ) AS rownum FROM contacts ) DELETE ...
If we look at the result set, we can easily understand thatBookNumber: 3andBookNumber: 4are duplicate rows. Previously, it was explained in detailhow to remove duplicates in SQL. We must delete them to keep the database consistent.
at/home/Code/GitHub/stonedb/sql/handler.cc:8230#2 0x000000000247ed8c in mysql_update (thd=0x7fdcec000bc0, fields=...,values=...,limit=18446744073709551615,handle_duplicates=DUP_ERROR,found_return=0x7fe0c81c9c58,updated_return=0x7fe0c81c9c50)at/home/Code/GitHub/stonedb/sql/sql_update.cc...
开始我们拿sql到数据库查询平台查库执行计划,无奈这个平台有bug,delete语句无法查看,所以我们改成select,“应该”是一样。这个“应该”加了双引号,导致我们走了一点弯路。 EXPLAIN SELECT * from t_table_1 where task_id in (select id from t_table_2 where uid = 1) ...
开始我们拿sql到数据库查询平台查库执行计划,无奈这个平台有bug,delete语句无法查看,所以我们改成select,“应该”是一样。这个“应该”加了双引号,导致我们走了一点弯路。 EXPLAINSELECT*fromt_table_1wheretask_idin(selectidfromt_table_2whereuid=1)
at/home/Code/GitHub/stonedb/sql/handler.cc:8230#2 0x000000000247ed8c in mysql_update (thd=0x7fdcec000bc0, fields=...,values=...,limit=18446744073709551615,handle_duplicates=DUP_ERROR,found_return=0x7fe0c81c9c58,updated_return=0x7fe0c81c9c50)at/home/Code/GitHub/stonedb/sql/sql_update.cc...