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In SQL Server, the WHERE clause is used to filter data based on specified conditions in a query. When working with character data types, such as VARCHAR or CHAR, you can use the WHERE clause with various operators to perform comparisons, string matching, and pattern matching.

Here are some commonly used operators and techniques for character data types in the WHERE clause:

1. Equality (=) Operator: The equality operator is used to match exact values. For example, if you have a column named "name" and you want to find all rows where the name is "John", you can use the following query:

SELECT * FROM table_name WHERE name = 'John';
This query will return all rows from "table_name" where the "name" column is exactly equal to 'John'.

2. LIKE Operator: The LIKE operator is used for pattern matching. It allows you to search for values that match a specific pattern using wildcard characters. The '%' character represents any sequence of characters, and '_' represents any single character. For example, if you want to find all rows where the name starts with 'J', you can use the following query:

SELECT * FROM table_name WHERE name LIKE 'J%';
This query will return all rows from "table_name" where the "name" column starts with 'J'.

3. IN Operator: The IN operator is used to specify multiple values in a WHERE clause. It allows you to filter rows where the value of a column matches any of the specified values. For example, if you want to find all rows where the name is either 'John' or 'Jane', you can use the following query:

SELECT * FROM table_name WHERE name IN ('John', 'Jane');
This query will return all rows from "table_name" where the "name" column is either 'John' or 'Jane'.

4. Comparison Operators: You can also use comparison operators such as greater than (>), less than (<), greater than or equal to (>=), and less than or equal to (<=) to compare character data. For example, if you want to find all rows where the name comes after 'J' alphabetically, you can use the following query:

SELECT * FROM table_name WHERE name > 'J';

This query will return all rows from "table_name" where the "name" column is alphabetically greater than 'J'.

These are some of the commonly used techniques for filtering character data in the WHERE clause of a SQL Server query. You can combine these operators and techniques to create more complex and specific conditions as per your requirements.