Gbase8s database select Clause 1

WHERE The clause is GBase 8s Extended connection specifies the connection condition , To conform to ANSI After specifying the connection filter , And for

Data specify search criteria ;

stay WHERE Use condition in Clause

stay WHERE clause , You can use these simple conditions or compare ：

Relational operator conditions

IN or BETWEEN . . . AND

IS NULL or IS NOT NULL

LIKE or MATCHES

You can also visit WHERE Used in clauses SELECT sentence ; This is called a subquery . In subquery , The following WHERE Clause

The operator is valid ：

IN or EXISTS

ALL、ANY or SOME

For more information , see also Conditions .

stay WHERE clause , The aggregate function is not valid , Unless it is part of a subquery , Or from the parent query

On the list of , And WHERE Clause in HAVING In a subquery within a clause .

Relational operator conditions

If the expression on each side of the relational operator satisfies the relationship specified by the expression , Then the relational operator condition is satisfied . The following words

Sentence use is greater than （

） And equal to （

=） Relational operator ：

SELECT order_num FROM orders

WHERE order_date > ‘6/04/08’;

SELECT fname, lname, company

FROM customer

WHERE city[1,3] = ‘San’;

‘San’ You need to put single quotes , Because the substring comes from the character column . see also Relational operator conditions .

WHERE Space string and empty string in clause

about LVARCHAR、NVARCHAR or VARCHAR Column , Specifies that the column value is equal to an empty string with WHERE Son

Query of sentence （

WHERE varlength_col = ‘’

） The result set returned , And among them WHERE Clause specifies equal to space （ASCII 32） The same query for character strings is

Same

for example , If varlength_col It's the type VARCHAR、NVARCHAR or LVARCHAR, Then

WHERE The clause example is functionally identical to specifying an equal to an empty string WHERE Clause ：

WHERE varlength_col = ’ ’

WHERE varlength_col = ’ ’

WHERE varlength_col = ’ ’

therefore , For built-in variable length character data types , Between an empty string and a string consisting entirely of one or more white space characters

between , There is no difference between .（ However , Please note that , Query filter

WHERE varlength_col IS NULL

Not equivalent to the previous WHERE Example of clause , And if varlength_col The value is NULL, Returns a different

Result set