UNION ALL SELECT column1 ,column2 ,…… FROM table2 [WHERE condition] 说明:UNION在合并两个或多个集合时会执行去重操作,而UNION ALL则直接将两个或者多个结果集合并,不执行去重。 另外,执行去重会消耗大量的时间,因此,在一些实际应用场景中,如果通过业务逻辑已确认了两个集合不存在重重复数据时,可直接用UNIO...
SQLite 多表查询重复记录 sql多表联合查询 去重,一,表的加法表的加法是指通过关键字union将格式相同的表按照行合并在一起,合并后的表会自动去重;使用关键字unionall可保留重复行,将两个表去重合并语句如下:select<列名1>,<列名2>...from<表1>uni
1.union的用法,单独用union时,合并后的表会删除重复数据 select <列名1>,<列名2> from <表1> union select <列名1>,<列名2> from <表2>; 2、union all的用法,用union all时,合并后的数据保留所有值,不删除重复项 select <列名1>,<列名2> from <表1> union all select <列名1>,<列名2> from <...
SELECTcolumn1,column2,……FROMtable1[WHEREcondition]UNIONALLSELECTcolumn1,column2,……FROMtable2[WHEREcondition] 说明:UNION在合并两个或多个集合时会执行去重操作,而UNION ALL则直接将两个或者多个结果集合并,不执行去重。 另外,执行去重会消耗大量的时间,因此,在一些实际应用场景中,如果通过业务逻辑已确认了两...
The columns in everySELECTstatement must also be in the same order UNION Syntax SELECTcolumn_name(s)FROMtable1 UNION SELECTcolumn_name(s)FROMtable2; UNION ALL Syntax TheUNIONoperator selects only distinct values by default. To allow duplicate values, useUNION ALL: ...
The following examples use UNION to combine the results of the same table to demonstrate the effects of ALL and parentheses when using UNION. The first example uses UNION ALL to show duplicated records and returns each row in the source table three times. The second example uses UNION without...
CREATE TABLE TestBatch (ColA INT PRIMARY KEY, ColB CHAR(3)); GO INSERT INTO TestBatch VALUES (1, 'aaa'); INSERT INTO TestBatch VALUES (2, 'bbb'); INSERT INTO TestBatch VALUSE (3, 'ccc'); -- Syntax error. GO SELECT * FROM TestBatch; -- Returns no rows. GO In the following...
In SQL, the Self JOIN operation allows us to join a table with itself, creating a relationship between rows within the same table. Let's look at an example. SELECT C1.first_name AS FirstPerson, C2.first_name AS SecondPerson, C1.country FROM Customers C1, Customers C2 WHERE C1.country...
H. Using UNION of three SELECT statements to show effects of ALL and parentheses The following examples use UNION to combine the results of the same table to demonstrate the effects of ALL and parentheses when using UNION. The first example uses UNION ALL to show duplicated records and returns...
If the table is an updatable ledger table, the ledger view is created as a union on the table and its history table. Each row in the ledger view represents either the creation or deletion of a row version in the ledger table. The ledger view contains all columns of the ledger table, ...