Question

Is this incorrect, can’t we pass the table name to a select query dynamically?

This is giving me a error ‘Must declare the table variable @TblName’

DECLARE @TblName VARCHAR(30)
SET @TblName = 'User'
SELECT * 
FROM @TblName

Answer 1

You need to create a dynamic SQL query, preferably using the QUOTENAME function. You can avoid any issues from malicious input by using QUOTENAME function.

Here is a sample script that illustrates how to query a table by creating a dynamic SQL query by passing in a table name. You can change the table name by value to the variable @tablename.

Create and insert script for sample:

CREATE TABLE sample
(
    id INT NOT NULL
);

INSERT INTO sample (id) VALUES
  (1),
  (2),
  (3),
  (4),
  (5),
  (6);

Dynamic SQL script:

DECLARE @execquery AS NVARCHAR(MAX)
DECLARE @tablename AS NVARCHAR(128)

SET @tablename = 'sample'
SET @execquery = N'SELECT * FROM ' + QUOTENAME(@tablename)

EXECUTE sp_executesql @execquery

Demo:

Click here to view the demo in SQL Fiddle.

Suggested read:

The Curse and Blessings of Dynamic SQL