The SQL Where Clause is used to specify a condition while fetching data from a single table or multiple tables are combined together. When a particular condition is satisfied, it returns the desired value from the table. The Where clause should be used to filter records and to fetch only necessary records from the table. The WHERE clause in SQL can be used along with all statements like SELECT, UPDATE, INSERT, etc.
The basic syntax of Where clause in SQL can be given as:
SELECT column1, column2, columnN' FROM table_name WHERE [condition]
You can make the condition more specific by using different comparison or logical operators like equal to, not, etc. Here is a list of comparison operators in SQL.
|>=||Greater than or equal|
|<=||Less than or equal|
|BETWEEN||Defines a certain range|
|LIKE||Search for a pattern|
|IN||To specify multiple possible values for a column|
The SELECT statement in SQL is used to query data from a database, but it returns all records from the queried database. However, there is a time when we have to restrict the query result to a specified condition. It is when Where clause in SQL comes handy. A simple syntax using SELECT and Where clause can be written as:
SELECT * FROM tableName WHERE Condition;
Here, SELECT is the most common statement that is used to fetch the data from the table. The WHERE keyword restricts the query result and condition is the filter applied to the query results. The filter could be a specific range or value or sub-query. Here is one quick example for your reference, how to specific condition using Where clause in SQL.
SELECT * FROM 'members' WHERE 'membership_number' = 1;
Take an example where we want to give personal details of a member whose membership number is one then we can use the given syntax for the same purpose. The objective of Where clause in SQL is:
SELECT column-names FROM table-name WHERE condition
The SELECT statement in SQL is used to query a database that lists all the records from a table. If you want to restrict your research, then you should combine it with other SQL clauses and WHERE clause is one of the most common examples that restricts the query result based on a specified condition. If you want to work with SQL databases, then it is necessary having hands-on expertize on SELECT and WHERE clauses otherwise things will not work well for you.
UPDATE table-name SET column-name =value WHERE condition
One of the most popular examples when working with SQL is an Update command that is used to update the existing records within a Table. This is an action query that can be applied to a set of records based on conditions you specify. This is taken as one of the most powerful features of RDBMS because you have the flexibility to modify multiple records together. A depth understanding of the Update Query helps you in improving the performance of a database application instead of performing all changes one by one manually in the code. Also, the maintenance of changes is much easier than you ever think of.
With update command in SQL, you can work on multiple records together and WHERE clause in between to specify some condition. Here, are the possible uses of Update Query within a database –
DELETE table-name WHERE Condition
The DELETE statement in SQL is used to delete a table or particular entry from the table based on the specified condition. It will only delete the entries from the table, not the table schema. If you want to delete the entire table from the database along with its structure, then you should use the truncate commands in this case.
SQL Operators are used to specifying conditions within an SQL statement and work as a conjunction to join various conditional statements. You can also use operators in SQL statements. Here is a list of operators that are frequently used by SQL statements:
There is a list of comparison operators in SQL that are listed below:
Following listed logical operators are frequently used by the SQL statements:
Following arithmetic operators are used by the SQL statements:
With the help of SQL queries, we may choose specific data from bulk data files. It is obvious that we cannot store the whole data in a single data but we should use multiple tables to store data logically. You can combine data from multiple tables to a single table or perform operations on multiple tables as required. It is all possible with the help of SQL operators. Moving ahead, let us see how where clause and operators can be used together.
A WHERE clause in SQL can be used with AND operator, if all filter criterion specified, are met. Consider an example where we want to get the complete list of movies that were released in 2008. You can use the following query for this purpose:
SELECT * FROM 'movies' WHERE 'category_id' = 2 AND 'year_released' = 2008 ;
Here, we can combine two or more conditions to make the query result more specific and accurate. For the above example, it has to meet two conditions, one is category ID and other is movie released time. The other common operator that we can use with WHERE clause is OR logical operator.
Here is one operator that can be used to WHERE clause in SQL. For AND operator, both conditions should be justified to process the final value. At the same time, when we are using the OR operator, even if one condition meets, the final value is calculated. Here is a quick example for your reference.
SELECT * FROM 'movies' WHERE 'category_id' =1 OR 'category_id' = 2 ;
The following query will process all records either from category 1 or category 2. If we are using AND operator, then the movie name should be given in both the categories. These operators can be combined with queries as per the requirement.
The WHERE clause when combined with IN operator in SQL, it will fetch results whose values are given within the IN keywords. It makes the result more specific but redundant sometimes. Here is one quick example for your reference.
SELECT * FROM 'members' WHERE 'membership_number' IN (1,2,3);
The given query will fetch records whose membership number is either 1,2 or 3. In the same way, you can define category ID or column name as per the requirement.
The WHERE clause when combined with NOT IN operator in SQL, it will not affect the rows whose values are given within the NOT IN keyword. It makes the result more specific but redundant sometimes. It may create confusion so try using it carefully. Here is one quick example for your reference.
SELECT * FROM 'members' WHERE 'membership_number' NOT in (1,2,3);
The given query will fetch records whose membership number is not 1,2 or 3.
Equal to, less than, not equal to, are a few comparison operators that can be used with the WHERE clause.
EQUAL TO (=)
SELECT * FROM 'members' WHERE 'gender' = 'female';
The given query will fetch all records whose gender is equal to the female. This is a common operator that can be used frequently as per the requirement.
GREATER THAN (>)
Here, you can fetch records whose value is greater than the given value. For example, you want to fetch records where payment paid is greater than 2000. For this purpose, you can use the following query.
SELECT * FROM 'payments' WHERE 'amount_paid' > 2000;
It will quickly show a list of payment that is above 2000 and easy to analyze by anyone. In this way, you can save your time where you don’t have to analyze the whole table, but a few entries can work great for you.
NOT EQUAL TO (<>)
SELECT * FROM 'movies' WHERE 'category_id' <> 1;
The given query selects movies whose category ID is not equal to one. It works opposite to the Equal to an operator.
The blog for SQL where clause gave you a perfect idea of how to use the clause within the query. It tells you about the meaning and necessity of WHERE clause and how to use it in the best way with examples. Also, it explains to you what will happen when the WHERE clause is combined with logical and comparison operators.
Once you have gone through all the topics, it is the time to practice certain problems and enhance your skillset. For this purpose, you can join the SQL certification course with JanBask Training and get certified with us. We help you in becoming a valuable IT resource for whom getting jobs with attractive salary packages is easier. All the Best!
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