"limit" query in Oracle database

Note: For technical discussion only, do not use for other purposes, all consequences have nothing to do with me.

We all know that the limit function is suitable for mysql database and cannot be used in Oracle database. When we need to use paging query, we can replace it with other methods.

Distinguish single and double quotation marks in Oracle database

Method 1: Not equal method (general method)

select * from user_tab_columns where table_name='ADMIN' and rownum = 1 and column_name<>'UNAME'

Use the unequal sign to invert, where rownum=1 outputs one row, if you want to output two rows, rownum<3.

You can also use not in to exclude

In the above way of writing, if there are too many table names to be excluded, the statement will be very long. There is a better way, using the not in keyword, only need to put the table to be excludedJust write the name directly.

select * from user_tab_columns where table_name='ADMIN' and rownum = 1 and column_name not in('ADMIN','MD5')

Method 2: Alias ​​method

Aliases can only be used for field names, not for table names

select * from (select column_name,rownum n from user_tab_columns where table_name= 'ADMIN') where n=2

rownum n is an alias, and the parentheses are subqueries. I think this statement is to execute the following where first, and then query the inside.

Extended Oracle related query statement:

select * from all_tables query all tables

select * from user_tables Query all tables created by the current user

select * from all_tab_columns query all fields

select * from user_tab_columns Query all tables created by the current user

select * from v$version find out version