Difference between filtering queries in JOIN and WHERE?

Question

In SQL I am trying to filter results based on an ID and wondering if there is any logical difference between

SELECT value  FROM table1  JOIN table2 ON table1.id = table2.id  WHERE table1.id = 1 

and

SELECT value  FROM table1  JOIN table2 ON table1.id = table2.id AND table1.id = 1 

To me, it seems as if the logic is different though you will always get the same set of results but I wondered if there were any conditions under which you would get two different result sets (or would they always return the exact same two result sets)

Answer 1

The answer is NO difference, but:

I will always prefer to do the following.

• Always keep the Join Conditions in ON clause
• Always put the filter's in where clause

This makes the query more readable.

So I will use this query:

SELECT value FROM table1 INNER JOIN table2         ON table1.id = table2.id WHERE table1.id = 1 

However when you are using OUTER JOIN'S there is a big difference in keeping the filter in the ON condition and Where condition.

Logical Query Processing

The following list contains a general form of a query, along with step numbers assigned according to the order in which the different clauses are logically processed.

(5) SELECT (5-2) DISTINCT (5-3) TOP(<top_specification>) (5-1) <select_list> (1) FROM (1-J) <left_table> <join_type> JOIN <right_table> ON <on_predicate> | (1-A) <left_table> <apply_type> APPLY <right_table_expression> AS <alias> | (1-P) <left_table> PIVOT(<pivot_specification>) AS <alias> | (1-U) <left_table> UNPIVOT(<unpivot_specification>) AS <alias> (2) WHERE <where_predicate> (3) GROUP BY <group_by_specification> (4) HAVING <having_predicate> (6) ORDER BY <order_by_list>; 

Flow diagram logical query processing

• (1) FROM: The FROM phase identifies the query’s source tables and processes table operators. Each table operator applies a series of sub phases. For example, the phases involved in a join are (1-J1) Cartesian product, (1-J2) ON Filter, (1-J3) Add Outer Rows. The FROM phase generates virtual table VT1.

• (1-J1) Cartesian Product: This phase performs a Cartesian product (cross join) between the two tables involved in the table operator, generating VT1-J1.

• (1-J2) ON Filter: This phase filters the rows from VT1-J1 based on the predicate that appears in the ON clause (<on_predicate>). Only rows for which the predicate evaluates to TRUE are inserted into VT1-J2.
• (1-J3) Add Outer Rows: If OUTER JOIN is specified (as opposed to CROSS JOIN or INNER JOIN), rows from the preserved table or tables for which a match was not found are added to the rows from VT1-J2 as outer rows, generating VT1-J3.
• (2) WHERE: This phase filters the rows from VT1 based on the predicate that appears in the WHERE clause (). Only rows for which the predicate evaluates to TRUE are inserted into VT2.
• (3) GROUP BY: This phase arranges the rows from VT2 in groups based on the column list specified in the GROUP BY clause, generating VT3. Ultimately, there will be one result row per group.
• (4) HAVING: This phase filters the groups from VT3 based on the predicate that appears in the HAVING clause (<having_predicate>). Only groups for which the predicate evaluates to TRUE are inserted into VT4.
• (5) SELECT: This phase processes the elements in the SELECT clause, generating VT5.
• (5-1) Evaluate Expressions: This phase evaluates the expressions in the SELECT list, generating VT5-1.
• (5-2) DISTINCT: This phase removes duplicate rows from VT5-1, generating VT5-2.
• (5-3) TOP: This phase filters the specified top number or percentage of rows from VT5-2 based on the logical ordering defined by the ORDER BY clause, generating the table VT5-3.
• (6) ORDER BY: This phase sorts the rows from VT5-3 according to the column list specified in the ORDER BY clause, generating the cursor VC6.

it is referred from book "T-SQL Querying (Developer Reference)"