Also, you may want to test the performance of each of these “SQL update from select” methods. Some methods may be much faster than others, as they depend on your tables and the quantity of data. Let’s take a look. Prepare Our Sample Data We’ll prepare some sample data to use in...
UPDATE A INNER JOIN (SELECT B.B1 as B1,B.B2 as B2,C.C1 as C1 from B LEFT JOIN C on B.B3=C.C3) as t ON A.A3=t.B1 set A.A1=t.B2, A.A2=t.C1; UPDATE tb_bookcase INNER JOIN (SELECT tb_bookinfo.rid as rid,tb_bookinfo.bookname,department.name LEFT JOIN department on tb...
UPDATE C_Route test_to SET test_to.RouteFlg = test_from.NoFlg FROM C_Route test_to JOIN C_Route test_from ON (test_to.RouteFlg = test_from.YesFlg AND test_to.CustomerID = test_from.CustomerID AND test_to.StartClientID = test_from.StartClientID AND test_...
update select用法 sql`UPDATE SELECT` 是 SQL 中的一个语句,用于根据一个查询的结果来更新另一个表中的数据。它的语法如下: ```sql UPDATE 目标表 SET 列1 = 值1, 列2 = 值2, ... FROM (SELECT 列1, 列2, ... FROM 源表 WHERE 条件) AS 临时表 WHERE 目标表.主键 = 临时表.主键; ``` ...
在SQL 中,表连接(left join、right join、inner join 等)常常用于 select 语句,其实在 SQL 语法中,这些连接也是可以用于 update 和 delete 语句的,在这些语句中使用 join 还常常得到事半功倍的效果。 Update T_OrderForm SET T_OrderForm.SellerID =B.L_TUserID FROM T_OrderForm A LEFT JOIN T_Product...
在SQL中，使用UPDATE语句可以修改表中的数据，而SELECT语句则用于检索数据。为了同时更新一个表中的数据并基于另一个表中的特定值，可以将这两个语句结合起来。例如，考虑如下SQL语句：update name set zfen = (select unique ROUND(AVG(syl),2) from sp_syl1 where xm='宋云亮')这段SQL语句的目的...
UPDATE Table1 SET Column1 = (SELECT ColumnFromTable2 FROM Table2 WHERE Table1.PrimaryKeyColumn = Table2.PrimaryKeyColumn)WHERE EXISTS (SELECT 1 FROM Table2 WHERE Table1.PrimaryKeyColumn = Table2.PrimaryKeyColumn);在这个例子中，子查询 (SELECT ColumnFromTable2 FROM Table2 WHERE Table1.Primary...
如果你的 SQL Server 版本或场景不允许使用 UPDATE ... FROM 语法，你可以考虑以下替代方法：使用 JOIN：UPDATE e SET e.Salary = (SELECT sa.NewSalary FROM SalaryAdjustments sa WHERE e.EmployeeID = sa.EmployeeID)WHERE EXISTS (SELECT 1 FROM SalaryAdjustments sa WHERE e.EmployeeID = sa.EmployeeID)...
第一步,词法分析,一条SQL语句由多个字符串组成,词法分析将提取关键字(比如SELECT,WHERE)、表名、字段名、查询条件等。 第二步,语法分析,判断输入的SQL是否正确,是否符合MySQL的语法。 需要注意的是:判断查询的字段在表中是否存在,也是在分析器这里进行。