SQL Server Learning (2)

1.Top Query Statements

SELECT TOP n < column name table > from < table name > [Query condition]

Used to get the number of data bars returned by the rule.

SELECT TOP N PERCENT < list name > from < table name > [Query condition] Indicates the number of data bars for which the previous percentage was obtained.

2.LIKE operator

Query the records in the database by using a wildcard character.

_ Denotes matching with any single character

% indicates a match to a string containing one or more characters

[] matches any single character in a specific range (for example, [a-f]) or a specific set (for example, [abcdef]).

[^] or [!]  Matches any single character other than a specific range (for example, [^a-f]) or a specific set (for example, [^abcdef]).   

Escape identifier

For special characters appearing in strings: '% ', ' [', ' [] ', ' _ ' can use ' [] ' to include them, so that they are treated as ordinary characters.

Select 1 where ' aa_ssd ' like '%[_]% '

Use the characters immediately following the escape to make the escaped character. The character following the escape is equivalent to the escape character in the string ' \ '.

SELECT * from Test_course where name like '%\_% ' escape ' \ '

SQL Server Learning (2)