To give you context, I am entering the quantity of elements detected in a sample and, if the quantity of an element is not detected, then I must be able to identify that an element was tested, but not detected, such as "ND". Now, a new scenario has arisen where I need to enter a decimal(5,2) OR a char(2) (i.e., one or the other, but never both) for each of those 30 columns.
but I have a MySQL database table that has many (e.g., 30) columns currently setup as the data type decimal(5,2). Best way to store different types of data in a single column, which should be query friendly - MySql.
All the similar seem to address a table that has a small number of columns affected by this issue.
Mysql union different column types how to#
In this tutorial, you have learned how to use the SQL Server UNION to combine rows from multiple queries into a single result set.To preface, similar questions have been asked, but I have not found any that address a table that has a large number of columns affected by this issue. To sort the result set returned by the UNION operator, you place the ORDER BY clause in the last query as follows: SELECTįor example, to sort the first names and last names of customers and staff, you use the following query: SELECT The query returns 1,455 rows as expected. To include the duplicate row, you use the UNION ALL as shown in the following query: SELECT
Mysql union different column types code#
1454 Code language: SQL (Structured Query Language) ( sql )īecause the result set of the union returns only 1,454 rows, it means that one duplicate row was removed. The staffs table has 10 rows and the customers table has 1,445 rows as shown in the following queries: SELECT COUNT (*) The following example combines names of staff and customers into a single list: SELECT See the following staffs and customers tables from the sample database: UNION and UNION ALL examples The following picture illustrates the main difference between UNION and JOIN: SQL Server UNION examples In other words, join appends the result sets horizontally while union appends the result set vertically. The join such as INNER JOIN or LEFT JOIN combines columns from two tables while the UNION combines rows from two queries. In other words, the UNION operator removes the duplicate rows while the UNION ALL operator includes the duplicate rows in the final result set. However, if you want to retain the duplicate rows, you need to specify the ALL keyword is explicitly as shown below: query_1 UNION ALLīy default, the UNION operator removes all duplicate rows from the result sets. The following Venn diagram illustrates how the result set of the T1 table unions with the result set of the T2 table: UNION vs.
The number and the order of the columns must be the same in both queries.The following are requirements for the queries in the syntax above: The following illustrates the syntax of the SQL Server UNION: query_1Ĭode language: SQL (Structured Query Language) ( sql ) SQL Server UNION is one of the set operations that allow you to combine results of two SELECT statements into a single result set which includes all the rows that belong to the SELECT statements in the union. Introduction to SQL Server UNION operator Summary: in this tutorial, you will learn how to use the SQL Server UNION to combine the results of two or more queries into a single result set.
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