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2025-04-05 Update From: SLTechnology News&Howtos shulou NAV: SLTechnology News&Howtos > Database >
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Query according to specific conditions
WEHRE LIKE BETWEEN IN ON OR.
UNION keyword
Join multiple tables together for row-level processing
SELECT expression1, expression2,... Expression_n
FROM tables
[WHERE conditions]
UNION [ALL | DISTINCT]
SELECT expression1, expression2,... Expression_n
FROM tables
[WHERE conditions]
Parameter description
Expression1, expression2,... Expression_n: the column to retrieve.
Tables: the data table to retrieve.
WHERE conditions: optional, search condition.
DISTINCT: optionally, delete duplicate data in the result set. By default, the UNION operator has removed duplicate data, so the DISTINCT modifier has little effect on the result.
ALL: optional, returns all result sets, including duplicate data.
Sort ORDER BY
Grouping GORUP BY+HAVING
Filter DISTINCT
Join query SQL92/SQL99
The only difference: external connection
Left outside connection LEFT JOIN
Right external connection RIGHT JOIN
Paging query
Original
SELECT FROM
SELECT ROWNUM NUT,T. FROM
(SELECT FROM EMP ORDER BY SAL) T WHERE ROWNUM5
Now
SELECT FROM EMP LIMIT 1,10
Where SELECT * FROM EMP LIMIT N M; N represents the starting position M represents several records in a page.
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