# WHERE Clause
WHERE Clause

When you need to query data from a table based on specified conditions, you can add a **WHERE** clause to the SELECT statement to filter out unnecessary data. The **WHERE** clause forms an expression for row selection and is used to obtain data based on specified conditions. Values in the table are returned only when the specified conditions are met.

## **Syntax**

```plaintext
""SELECT 
{ * | [column, ...] }
[ FROM from_item [, ...] ]
[ WHERE condition ];
```

## **Parameter Description**

* **WHERE clause**
    
    The **WHERE** clause forms an expression for row selection to narrow down the query range of the SELECT statement. Comparison operators or logical operators, such as >, <, =, LIKE, or NOT, can be used in the **WHERE** clause.
    
* **condition**
    
    **condition** indicates any expression that returns a value of Boolean type. Rows that do not meet this condition will not be retrieved.
    

## **Examples**

Use logical operators to read data from the **customer\_t1** table.

* **AND**
    
    Locate the row where the value of **c\_customer\_id** is **hello** and that of **c\_customer\_sk** is **3869**.
    
    ```plaintext
    ""openGauss=# SELECT * FROM customer_t1 WHERE  c_customer_sk = 3869 AND c_customer_id = 'hello';
     c_customer_sk | c_customer_id | c_first_name | c_last_name | amount
    ---------------+---------------+--------------+-------------+--------
              3869 | hello         | Grace        |             |   1000
              3869 | hello         | Grace        |             |   1000
              3869 | hello         |              |             |
              3869 | hello         |              |             |
    (4 rows)
    ```
    
* **OR**
    
    Locate the row where the value of **c\_customer\_sk** is greater than **6985** or that of **c\_customer\_id** is **hello**.
    
    ```plaintext
    ""openGauss=# SELECT * FROM customer_t1 WHERE  c_customer_sk > 6985 OR c_customer_id = 'hello';
    c_customer_sk | c_customer_id | c_first_name | c_last_name | amount
    ---------------+---------------+--------------+-------------+--------
              3869 | hello         | Grace        |             |   1000
              3869 | hello         | Grace        |             |   1000
              3869 | hello         |              |             |
              3869 | hello         |              |             |
              9976 | world         | James        |             |   5000
    (5 rows)
    ```
    
* **NOT NULL**
    
    Locate the row where the value of **c\_last\_name** is not empty in the **customer\_t1** table.
    
    ```plaintext
    ""openGauss=# SELECT * FROM customer_t1 WHERE  c_last_name IS NOT NULL;
     c_customer_sk | c_customer_id | c_first_name | c_last_name | amount
    ---------------+---------------+--------------+-------------+--------
    (0 rows)
    ```
    
* **BETWEEN**
    
    Locate the row where the value of **c\_customer\_sk** is between **4000** and\*\* 9000\*\*.
    
    ```plaintext
    ""openGauss=# SELECT * FROM customer_t1 WHERE  c_customer_sk  BETWEEN 4000 AND 9000;
     c_customer_sk | c_customer_id | c_first_name | c_last_name | amount
    ---------------+---------------+--------------+-------------+--------
              6985 | maps          | Joes         |             |   2200
              4421 | Admin         | Local        |             |   3000
    (2 rows)
    ```
    

[Previous](https://docs.opengauss.org/en/docs/latest/docs/BriefTutorial/expressions.html)