Gbase8s database union operator

take UNION Operators are placed in two SELECT Statements to combine queries into a single query .

have access to UNION Operator will be several SELECT Statements are strung together . The corresponding item does not need to have the same name . It can be done by

Omit ALL Keyword to exclude duplicate lines .

In this version GBase 8s in , Include in UNION Operator supports the combined query of numeric fields and numeric strings

Inquiry . The returned result is DECIMAL(16) or DECIMAL(32) （ Depends on the length of the returned value ） data type .

for example ：

SELECT 123 FROM tab1 UNION SELECT ‘456’ FROM tab2;

The next example assumes tab1 In the table colid As a INT type ：

SELECT col1id FROM tab1 UNION SELECT ‘111’ FROM tab2;

Use UNION You can also directly NULL Value and other types of column values , Without coercion NULL

Data type of . The type of the returned result is the same as NULL The data types of other types of values corresponding to values are consistent .

for example , In the following example, it is assumed that tab2 In the table colid The type of VARCHAR：

SELECT NULL as a1 FROM tab1

UNION SELECT colname FROM tab2

INTO tab3;

The database will automatically NULL The type of is converted to colname The data type of the column VARCHAR. see tab3

List the information ：

info columns for tab3;

Return as follows ：

Column name Type Nulls

A1 varchar(10)