![]() ![]() To perform more complex matches such as ranges, you use the searched CASE statement. The simple CASE statement only allows you to compare a value with a set of distinct values. The following statement returns the shipping time of the customer 112: SELECT Code language: SQL (Structured Query Language) ( sql )ġ row in set ( 0.00 sec) Code language: SQL (Structured Query Language) ( sql ) Searched CASE statement This statement calls the stored procedure and passes the customer number 112: CALL GetCustomerShipping( Code language: SQL (Structured Query Language) ( sql ) The following flowchart demonstrates the logic of the CASE statement for determining the shipping time: The customers from other countries have 5-day shipping. If the customer locates in Canada, the shipping time is 3-day shipping. ![]() If the customer locates in USA, the shipping time is 2-day shipping. Second, use the simple CASE statement to determine the shipping time based on the country of the customer. The GetCustomerShipping() stored procedure accepts two parameters: pCustomerNumber as an IN parameter and pShipping as an OUT parameter.įirst, select the country of the customer from the customers table by the input customer number. The following stored procedure illustrates how to use the simple CASE statement: DELIMITER $$ The simple CASE statement tests for equality ( =), you cannot use it to test equality with NULL because NULL = NULL returns FALSE. To avoid the error when the case_value does not equal any when_value, you can use an empty BEGIN END block in the ELSE clause as follows: CASE case_value The statements can be one or more SQL statements, and cannot have zero statements. Note that the case_value can be a literal value or an expression. When the ELSE clause does not exist and the CASE cannot find any when_value equal to the case_value, it issues an error: Case not found for CASE statement Code language: PHP ( php ) If CASE cannot find any when_value equal to the case_value, it executes the else-statements in the ELSE clause if the ELSE clause is available. When the CASE finds a case_value equal to a when_value, it executes statements in the corresponding THEN clause. In this syntax, the simple CASE statement sequentially compares the case_value is with the when_value1, when_value2, … until it finds one is equal. The following is the basic syntax of the simple CASE statement: CASE case_valueĮND CASE Code language: SQL (Structured Query Language) ( sql ) ![]() Note that if you want to add the if-else logic to an SQL statement, you use the CASE expression which is different from the CASE statement described in this tutorial. The CASE statement has two forms: simple CASE and searched CASE statements. The CASE statements make the code more readable and efficient. Introduction to MySQL CASE statementīesides the IF statement, MySQL provides an alternative conditional statement called the CASE statement for constructing conditional statements in stored procedures. This is also why it can be important to ensure that your test suites use the same version of the JDBC driver and the same version of your database (even when it is convenient and tempting to run tests against, say, an in-memory DB like H2 or a local DB like Derby or SQLite).Summary: in this tutorial, you will learn how to use MySQL CASE statements to construct complex conditional statements inside stored procedures. But it’s worth checking what types actually come back from a given SQL operation (in the REPL) – and it’s also worth being a bit more careful (or at least forgiving) in terms of comparisons you perform on data coming back from the database (e.g., as John noted above, using = for numeric equality instead of = unless you know exactly what types you are dealing with).Ĭomputed values – as in your CASE expression – are particularly “vulnerable” since the database may use a “larger” type than you expect to avoid potential truncation/overflow. I wouldn’t say you can’t trust the types – for a given database and JDBC driver version, they are consistent. So I’m starting here with the hope that someone smarter than me has a clue This may not be/is probably not a Clojure-specific problem but I don’t know very much about databases or any Java so I cannot recreate the problem outside of Clojure using jdbc. Query where `int_field` is returned from a CASE statement Create table with one integer field `int_field` Using the MySQL connection, the value returned is 1 and using the MariaDB connection, the value returned is 1M. It takes a db connection, creates a table with one integer field, inserts one row with the value 1 and then queries the table using a CASE statement that returns the row. The following function demonstrates the problem. And now queries with CASE statements that should return a Long instead return a BigDecimal. I need to change my database driver from MySQL 5.7.26 to the latest MariaDB driver 10.5.8.
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