原因:in在查询的时候,先查子查询的表B,然后将内表和外表做一个笛卡尔积,然后按照条件筛选,所以子查询表比较小的时候,in的速度较快; 而exists 是对外表A做loop循环,每次loop循环再对内表B进行查询,即我们先查询的不是子查询B的内容,而是查我们的主查询的表A,所以子查询表数据比较大的时候,exists的速度较快 n...
Nested Loop Join 适用于驱动表数据比较少,并且连接的表中有索引的时候。排序合并连接( Sort Merge Join),先将两个表中的数据基于连接字段进行排序,然后合并。Sort Merge Join 通常用于没有 索引,并且数据已经排序的情况,比较少见。哈希连接(Hash Join),将一个表的连接字段计算出一个哈希表,然后从另一个表中...
fopen ('DB_UTL_DIR', 'x.txt', 'r'); -->打开源文件用于读取数据 -- open a file to write outfile := UTL_FILE.fopen ('DB_UTL_DIR', 'out.txt', 'w'); -->创建目标文件用于存放数据 -- if the file to read was successfully opened IF UTL_FILE.is_open (infile) THEN -- loop ...
Can we use While loop in CTE? can we write DDL command in Stored Procedure? Can wildcards be used on datetime column? can you add colour to a fields output in T-SQL? Can you change the value of yes or no instead of true or false use data type (BIT) ? Can you have a TRY CATC...
DECLARE @loop INT; DECLARE @AccountDescription VARCHAR(50); DECLARE @AccountKey INT; DECLARE @AccountType VARCHAR(50); DECLARE @AccountCode INT; SELECT @loop = 0 BEGIN TRANSACTION WHILE (@loop < 300000) BEGIN SELECT @AccountKey = CAST(RAND() * 10000000 AS INT); SELECT @AccountDescription...
DECLARE @loop INT; DECLARE @AccountDescription VARCHAR(50); DECLARE @AccountKey INT; DECLARE @AccountType VARCHAR(50); DECLARE @AccountCode INT; SELECT @loop = 0 BEGIN TRANSACTION WHILE (@loop < 300000) BEGIN SELECT @AccountKey = CAST(RAND() * 10000000 AS INT); SELECT @AccountDescription...
insertintotestvalues(1,'a'); insertintotestvalues(1,'b'); insertintotestvalues(1,'c'); insertintotestvalues(2,'d'); insertintotestvalues(2,'e'); 效果1 : 行转列 ,默认逗号隔开 SQL Code 1 selectwm_concat(name) namefromtest;
2.2.2Preparing a Migration Plan This topic describes the process of how to create a migration plan. It identifies the sections to include in the migration plan, describes how to determine what to include for each section, and explains how to avoid the risks involved in a migration project. ...
Prevent infinite loop in VACUUM Fix failure after attaching a table as a partition, if the table had previously had inheritance children Fix input of ISO-8601 “extended” time format for types time and timetz For further details, please visitPostgreSQL’s release notes. ...
In a distributed transaction, execute_statement cannot be issued against a loopback linked server when the connection has multiple active result sets (MARS) enabled. If execute_statement returns data with the READTEXT statement, each READTEXT statement can return a maximum of 1 MB (1024 KB) of...