Difference between UNION and UNIONALL

Question

what the difference between UNION and UNIONALL?

Satyapriya Nayak · Answer

Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 UNION /* Style Definitions */ table.MsoNormalTable{mso-style-name:Table Normal;mso-tstyle-rowband-size:0;mso-tstyle-colband-size:0;mso-style-noshow:yes;mso-style-priority:99;mso-style-qformat:yes;mso-style-parent:;mso-padding-alt:0in 5.4pt 0in 5.4pt;mso-para-margin-top:0in;mso-para-margin-right:0in;mso-para-margin-bottom:10.0pt;mso-para-margin-left:0in;line-height:115%;mso-pagination:widow-orphan;font-size:11.0pt;font-family:Calibrisans-serif;mso-ascii-font-family:Calibri;mso-ascii-theme-font:minor-latin;mso-fareast-font-family:Times New Roman;mso-fareast-theme-font:minor-fareast;mso-hansi-font-family:Calibri;mso-hansi-theme-font:minor-latin;} The purpose of the SQL UNION query is to combine the results of two queries together. In this respect UNION is somewhat similar to JOIN in that they are both used to related information from multiple tables. One restriction of UNION is that all corresponding columns need to be of the same data type. Also when using UNION  only distinct values are selected (similar to SELECT DISTINCT ). The syntax is as follows: [SQL Statement 1] UNION [SQL Statement 2] Say we have the following two tables Table Store_Information store_name Sales Date Los Angeles $1500 Jan-05-1999 San Diego $250 Jan-07-1999 Los Angeles $300 Jan-08-1999 Boston $700 Jan-08-1999 Table Internet_Sales Date Sales Jan-07-1999 $250 Jan-10-1999 $535 Jan-11-1999 $320 Jan-12-1999 $750 and we want to find out all the dates where there is a sales transaction. To do so we use the following SQL statement: SELECT Date FROM Store_Information UNION SELECT Date FROM Internet_Sales Result: Date Jan-05-1999 Jan-07-1999 Jan-08-1999 Jan-10-1999 Jan-11-1999 Jan-12-1999 UNION ALL The purpose of the SQL UNION ALL command is also to combine the results of two queries together. The difference between UNION ALL and UNION is that while UNION only selects distinct values UNION ALL selects all values. The syntax for UNION ALL is as follows: [SQL Statement 1] UNION ALL [SQL Statement 2] Let's use the same example as the previous section to illustrate the difference. Assume that we have the following two tables Table Store_Information store_name Sales Date Los Angeles $1500 Jan-05-1999 San Diego $250 Jan-07-1999 Los Angeles $300 Jan-08-1999 Boston $700 Jan-08-1999 Table Internet_Sales Date Sales Jan-07-1999 $250 Jan-10-1999 $535 Jan-11-1999 $320 Jan-12-1999 $750 and we want to find out all the dates where there is a sales transaction at a store as well as all the dates where there is a sale over the internet. To do so we use the following SQL statement: SELECT Date FROM Store_Information UNION ALL SELECT Date FROM Internet_Sales Result: Date Jan-05-1999 Jan-07-1999 Jan-08-1999 Jan-08-1999 Jan-07-1999 Jan-10-1999 Jan-11-1999 Jan-12-1999 UNION is used to select information from two tables.But it selects only distinct records from both the table.  while UNION ALL selects all records from both the tables. Please refer the below links http://www.1keydata.com/sql/sqlunion.html http://www.1keydata.com/sql/sqlunionall.html Thanks /* Style Definitions */ table.MsoNormalTable{mso-style-name:Table Normal;mso-tstyle-rowband-size:0;mso-tstyle-colband-size:0;mso-style-noshow:yes;mso-style-priority:99;mso-style-qformat:yes;mso-style-parent:;mso-padding-alt:0in 5.4pt 0in 5.4pt;mso-para-margin-top:0in;mso-para-margin-right:0in;mso-para-margin-bottom:10.0pt;mso-para-margin-left:0in;line-height:115%;mso-pagination:widow-orphan;font-size:11.0pt;font-family:Calibrisans-serif;mso-ascii-font-family:Calibri;mso-ascii-theme-font:minor-latin;mso-fareast-font-family:Times New Roman;mso-fareast-theme-font:minor-fareast;mso-hansi-font-family:Calibri;mso-hansi-theme-font:minor-latin;}

Vulpes · Answer

The UNION operator combines the results of two or more compatible queries into a single result set which consists of all the rows from each query including duplicates. The UNION ALL operator does the same as UNION but excludes duplicate rows.