INTERSECT operator in SQL Server

In SQL Server (Transact-SQL), INTERSECT operator is used to return records in both data sets or SELECT statements. If a record is available only in one query and not in the other, it will be removed from the result set of INTERSECT.

INTERSECT query

Illustrate the result returned from INTERSECT query

Explanation: INTERSECT query will return records located in the blue fill area. These records are in both database1 and database2.

Each SELECT in INTERSECT must have the same number of columns in the result set with the same data type.

INTERSECT operator syntax

 SELECT b ieu_thuc1, bieu_thuc2, … bieu_thucn 
 FROM bang 
 [WHERE dieu_kien] 
 INTERSECT 
 SELECT bieu_thuc1, bieu_thuc2, … bieu_thucn 
 FROM bang 
 [WHERE dieu_kie n]; 

Variable name or variable value

bieu_thuc

The column or value you want to compare between the SELECT statements. They do not need to be in the same information field at each SELECT statement but the corresponding columns must have the same data.

state

Table wants to get records from there. Must have at least 1 table in the FROM clause.

WHERE dieu_kien

Option. Conditions must satisfy for the selected record.

Note:

1. Two SELECT statements must have the same number of expressions.
2. The corresponding column in each SELECT statement must have the same data type.
3. The INTERSECT operator returns only the general record between SELECT statements.

For example - with 1 expression

 SELECT sa npham_id 
 FROM sanpham 
 INTERSECT 
 SELECT sanpham_id 
 FROM hangtonk ho; 

In this example, if sanpham_id appears on both the sanpham and hangtonkho tables, it will be in the result set of INTERSECT.

Now add the WHERE condition to this query.

 SELECT sanph am_id 
 FROM sanpham 
 WHERE sanpham_id >= 50 
 INTERSECT 
 SELECT sanpham_id 
 FROM hangtonkho 
 WHERE soluong > 0; 

The first dataset will filter and return records in the dashboard and sanpham_id greater than or equal to 50. The second data set will filter from the hangtonkho table if the number is greater than 0.

For example - with multiple expressions

 SE LECT danhba_id, ho, ten 
 FROM danhba 
 WHERE ho = 'Anderson' 
 INTERSECT 
 SELECT nhanvien_id, ho, ten 
 FROM nh anvien; 

In this example, the query returns the result of the intersection of the two SELECT statements. If there is a record in the list of danhba that danhba_id , ho , ten danhba danhba_id , the name of the INTERSECT query will return those records.

For example - use ORDER BY

Use the ORDER BY clause with INTERSECT query to sort results.

 SELECT nhacun g_id, nhacung_ten 
 FROM nhacung 
 WHERE nhacung_id > 500 
 INTERSECT 
 SELECT congty_id, congty_ten 
 FROM congty 
 WHERE congty_ten in ('Apple', 'Microsoft', 'SQL Server') 
 ORDER BY 2; 

Because the column name in the two SELECT statements is different, it is easier to reference the column in the ORDER BY clause by their position in the result set. In the above example, we filter the result nhacung_ten / congty_ten in ascending order through the phrase ORDER BY 2.

Because the nhacung_ten / congty_ten is the 2nd in the result set.

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