{"id":22692,"date":"2018-08-11T05:15:43","date_gmt":"2018-08-11T05:15:43","guid":{"rendered":"https:\/\/data-flair.training\/blogs\/?p=22692"},"modified":"2021-03-10T21:25:41","modified_gmt":"2021-03-10T15:55:41","slug":"null-values-in-sql-union-clause","status":"publish","type":"post","link":"https:\/\/data-flair.training\/blogs\/null-values-in-sql-union-clause\/","title":{"rendered":"NULL Values In SQL | SQL UNION Clause"},"content":{"rendered":"

We often require to combine the large volumes of data available to us in order to deal with day-to-day analysis and problems. Most of the time we have data spread in multiple tables.<\/p>\n

To connect and collect all the data required by us, we often use various inbuilt functionalities.<\/p>\n

In SQL, we use the Join and Union clause for the same. In this clause, we will be discussing the working and the usage of the Union clause and at the same time, we will see how we will be handling the null values present in our data.<\/p>\n

Null values, if present in the data, can cause various logical and mathematical errors, so we need to be very cautious if we have null values in our database.<\/p>\n

Let us move forward and discuss the Union clause in detail.<\/p>\n

What is Union Clause in SQL and its Usage?<\/h3>\n

We use the union clause to get combined results from multiple select queries. We mostly use Union with two or more SQL select statements to combine the results they provide after querying the database.<\/p>\n

Some points to keep in mind:<\/p>\n

    \n
  1. Select statements within the union statement must have the same number of columns.<\/li>\n
  2. All of the columns must be of the same datatype.<\/li>\n
  3. The order in the select statements should be maintained.<\/li>\n<\/ol>\n

    Syntax of SQL Union Clause:<\/strong><\/p>\n

    SELECT * FROM tableName1\r\nUNION\r\nSELECT *  FROM tableName2;\r\n<\/pre>\n
    Demo Database<\/h3>\n
    Let us view our available tables in our database.
    \nTable 1:<\/strong><\/p>\n
    \"SQL<\/a><\/p>\n
    Table 2:<\/strong><\/p>\n
    \"SQL<\/a><\/p>\n
    Types of Union Clause and Examples<\/h3>\n
    Union Clause in SQL<\/h4>\n
    When we use the union clause, it returns only the distinct values from the returned query result.<\/p>\n
    Syntax of SQL Union Clause:<\/strong><\/p>\n
    SELECT * FROM tableName1\r\nUNION\r\nSELECT * FROM tableName2\r\n<\/pre>\n
     <\/p>\n
    \"SQL<\/a><\/p>\n
    Example 1:<\/strong> Let us view the collective post and name of employees.<\/strong>
    \nQuery:<\/strong><\/p>\n
    SELECT  post FROM dataflair_emp1\r\nUNION\r\nSELECT name_emp as name FROM dataflair_emp2\r\n<\/pre>\n
    \"SQL<\/a><\/p>\n
    SQL Union All Clause<\/h4>\n
    When we use the union all clause, we get all the possible details, i.e., repetitions are also included. When we use only UNION duplicate data is excluded.<\/p>\n
    Syntax:<\/strong><\/p>\n
    SELECT * FROM tableName1\r\nUNION ALL\r\nSELECT * FROM tableName2\r\n<\/pre>\n
     <\/p>\n
     <\/p>\n
    \"SQL<\/a><\/p>\n
    Example 1:<\/strong> Let us collect the email id\u2019s stored in both the DataFlair employee tables.<\/strong>
    \nQuery:<\/strong><\/p>\n
    SELECT  email FROM dataflair_emp1\r\nUNION All\r\nSELECT email as name FROM dataflair_emp2\r\norder by email\r\n<\/pre>\n
    \"SQL<\/a><\/p>\n
    SQL Union with Where clause<\/h4>\n
    When we use where with the union clause, we merge data that satisfies a condition. Conditions are passed in the where clause to get data according to the conditional statement.<\/p>\n
    Syntax:<\/strong><\/p>\n
    SELECT * FROM tableName1 Where condition\r\nUNION\r\nSELECT * FROM tableName2 Where condition ;\r\n<\/pre>\n
    Example 1:<\/strong> Let us find employee emails with age more than 27 and a salary less than 30000.<\/strong>
    \nQuery:<\/strong><\/p>\n
    SELECT  salary,email FROM dataflair_emp1 Where salary < 30000\r\nUNION All \r\nSELECT age,email as name FROM dataflair_emp2 where age > 27\r\norder by email\r\n<\/pre>\n
    \"SQL<\/a><\/p>\n
    Null values in UNION Clause<\/h3>\n
    When we use Union the values which are null are automatically included in the result.
    \nFirst Database after Modification:<\/strong>
    \nQuery :<\/strong><\/p>\n
    SELECT * FROM DataFlair_emp1 ;<\/pre>\n
    \"SQL<\/a><\/p>\n
    Example 1:<\/strong> Let us again try to view all the mail id\u2019s after entering null values in our database.<\/strong>
    \nQuery:<\/strong><\/p>\n
    SELECT  email FROM dataflair_emp1 \r\nUNION All \r\nSELECT email as name FROM dataflair_emp2 \r\norder by email\r\n<\/pre>\n
    \"SQL<\/a><\/p>\n
    Summary<\/h3>\n
    When we deal with voluminous data, we need certain combinations from time to time.<\/p>\n
    With the help of SQL Union clause, we can easily generate combinations of data with various conditions and orders.<\/p>\n
    Union provides us functionality to deal with both unique and duplicate types of data. When we deal with the union clause we need to take care of some points which we have already discussed above.<\/p>\n
    The essence lies in having the same type and same count of columns.<\/p>\n","protected":false},"excerpt":{"rendered":"
    We often require to combine the large volumes of data available to us in order to deal with day-to-day analysis and problems. Most of the time we have data spread in multiple tables. To...<\/p>\n","protected":false},"author":6,"featured_media":86858,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[66],"tags":[7314,9146,9149,11093,13500,13502,13584,13585],"class_list":["post-22692","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-sql","tag-is-not-null","tag-null-value-example","tag-null-values-in-sql","tag-queries-in-null-values","tag-sql-null-clause","tag-sql-null-value-example","tag-sql-union-all-with-where","tag-sql-union-clause-example"],"yoast_head":"\nNULL Values In SQL | SQL UNION Clause - DataFlair<\/title>\n<meta name=\"description\" content=\"NULL values in SQL, SQL Union Clause, Example of SQL UNION Clause, SQL UNION ALL With WHERE, UNION ALL Clause, null value example\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/data-flair.training\/blogs\/null-values-in-sql-union-clause\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"NULL Values In SQL | SQL UNION Clause - 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