What is a SQL pseudo-column?

Question

I accidentally coded SELECT $FOO..and received the error "Invalid pseudo-columns" $ FOO ".

I can not find any documentation for them. Is that what I should know?

Edit: This is a specific MS SQL Server question.

Answer 1

Pseudo-collancers are symbolic aliases for actual columns that have special properties, for example, $ IDENTITY is an alias for a column assigned IDENTITY, $ ROWGUID for a column assigned ROWGUIDCOL. It is used for indoor plumbing scenarios.

Answer 2

, Oracle: SQL Server!

, RobsonROX, output merge. $action , ​​ .

Answer 3

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Answer 4

Google this Oracle:

, . pseudocolumns, , .

, , $FOO, , psuedocolumn $FOO . "$ FOO" ( ), " $FOO". . , .

Answer 5

Pseudocolumns - , . Oracle ROWNUM, . SQL-, , , , , , Oracle.

Answer 6

ROWID Informix. 32- , , ( , , ), . SELECT * FROM SomeTable, ; SELECT ROWID, * FROM SomeTable, . ( ROWID , ROWID , ), -. -, - , , .

They can also be called by hidden columns, especially if they (unlike pseudo-columns) are actually stored in the database but not selected *; you need to specifically query the column to see it.

Answer 7

pseudo columns are false columns. any table will support pseudo-columns in the same way as its own column, strictly speaking, they are functions: 1.SYSDATE; 2.ROWNUM; 3.ROWID; 4.NEXTVAL; 5.CURRVAL; 6.LEVEL;