Question

sql *=运算符什么意思?

举个例子说明下
还有一个=*

Answer 1

FROM子句
对于每个SELECT子句，FROM子句是强制性的。FROM子句主要用来指定检索数据的来源，数据的来源可以是若干个表或视图，数据表之间或视图名之间用逗号分隔。下面是FROM子句的语法：

[ FROM { < table_source > } [ ,...n ] ]

< table_source > ::=

table_name [ [ AS ] table_alias ] [ WITH ( < table_hint > [ ,...n ] ) ]

| view_name [ [ AS ] table_alias ] [ WITH ( < view_hint > [ ,...n ] ) ]

| rowset_function [ [ AS ] table_alias ]

| user_defined_function [ [ AS ] table_alias ]

| derived_table [ AS ] table_alias [ ( column_alias [ ,...n ] ) ]

| < joined_table >

< joined_table > ::=

< table_source > < join_type > < table_source > ON < search_condition >

| < table_source > CROSS JOIN < table_source >

| [ ( ] < joined_table > [ ) ]

< join_type > ::=

[ INNER | { { LEFT | RIGHT | FULL } [OUTER] } ]

[ < join_hint > ]

JOIN

FULL [OUTER]：指定在结果集中包含左表或右表中不满足连接条件的行，并将对应于另一个表的输出列设为NULL。这是对通常由INNER JOIN返回的所有行的补充。说明按此处指定的方法指定外连接或在WHERE子句中使用旧式非标准的 *= 和 =* 运算符都是可行的。不能在同一语句中同时使用这两种方法。

Answer 2

=*/*=是SQL7.0时用的方法

此方法在多表连接时，会造成结果集不一至；在联机上也有说明，建议楼主不要使用此方法。用left join /right join替代

Answer 3

确定没写错？

Answer 4

反了，*=是左外连接，=*是右外连接