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MySQL Articles
Page 21 of 355
How to search multiple columns in MySQL?
Let us understand how to search multiple columns in MySQL −Note: We assume we have created a database named ‘DBNAME’ and a table named ‘tableName’.The ‘AND’ and ‘OR’ operators can be used, depending on what the user wants the search to return.Let us see that with the help of an example −ExampleSELECT colName FROM tableName WHERE my_col LIKE %$param1% AND another_col LIKE %$param2%;In the above example, the ‘AND’ operator is used.This means that both the clause has to match a record for the result to be returned.QuerySELECT colName FROM tableName WHERE my_col LIKE %$param1% OR another_col LIKE %$param2%;In the above ...
Read MoreSearching on Two Keys in MySQL
Let us understand how to search on two keys in MySQLSearching on two keys can be achieved using the ‘OR’ with the help of single key which is well optimized or using ‘AND’ which is well optimized. Let us see how searching on two different keys can be done combining it with ‘OR’ operation −SELECT field1_index, field2_index FROM tableName WHERE field1_index = '1' OR field2_index = '1'This is an optimized version of the query. It can also be done efficiently using the ‘UNION’ that combines the output of two separate ‘SELECT’ statements. Every ‘SELECT’ statement searches only for one key ...
Read MoreUsing User-Defined Variables in MySQL
Let us understand what user variables are and how they can be used in MySQL. We will also see the rules −User variables are written as @var_name. Here, the ‘var_name’ refers to variable name, which consists of alphanumeric characters, ., _, and $.A user variable name can contain other characters if they are quoted as a string or identifier.User-defined variables are session specific.A user variable which is defined by one client can’t be seen or used by other clients.But the only exception is that if a user has access to the Performance Schema user_variables_by_thread table, then that user can see ...
Read MoreThe Rows Holding the Group-wise Maximum of a Certain Column in MySQL
Let us understand how to find the rows that hold the group wise maximum of a specific column in MySQL −The syntax to find the rows that hold the group-wise maximum of a specific column in MySQL is as follows −SELECT colName1, colName2, colName3 FROM tableName s1 WHERE colName3=(SELECT MAX(s2. colName3) FROM tableName s2 WHERE s1. colName1= s2. colName1) ORDER BY colName1;Let’s say we have the following PRODUCT Table −+---------+----------+--------+ | Article | Warehouse| Price | +---------+----------+--------+ | 1 | North | 255.50 | | 1 | North | 256.05 | | ...
Read MoreMaximum of Column per Group in MySQL
Let us understand how to find the maximum of a column per group in MySQL −SELECT colName1, MAX(colName2) FROM tableName GROUP BY colName1 ORDER BY colName1;We will now see a live example. Let’s say we have a table PRODUCT −+---------+--------+ | Article | Price | +---------+--------+ | 1 | 255.50 | | 1 | 256.05 | | 2 | 90.50 | | 3 | 120.50 | | 3 | 123.10 | | 3 | 122.10 | +---------+--------+Following is the query to get the maximum of column per group −QuerySELECT Article, MAX(Price) AS MaxPrice FROM Product GROUP BY Article ORDER BY Article;Output+--------------+--------------+ | Article | MaxPrice | +--------------+--------------+ | 0001 | 256.05 | | 0002 | 90.50 | | 0003 | 123.10 | +--------------+--------------+
Read MoreMajor Contributors to MySQL
Let us see who the major contributors to MySQL are −Although Oracle Corporation and/or its affiliates own all copyrights in the MySQL server and the MySQL manual, we wish to recognize those who have made contributions of one kind or another to the MySQL distribution. Contributors are listed here, in somewhat random order −Gianmassimo Vigazzola − They helped with the initial port to Win32/NT.Per Eric Olsson − They provided for constructive criticism and real testing of the dynamic record format.Irena Pancirov − Helped with the Win32 port with Borland compiler. They also helped with the mysqlshutdown.exe and mysqlwatch.exe.David J. Hughes ...
Read MoreUpgrading MySQL Binary or Package-based Installations on Unix/Linux
Let us understand how MySQL binary and package-based installations can be upgraded in Unix or Linux. This can be done in-place as well as by using a logical upgrade method. Let us understand both these methods in brief −In place upgradeAn in−place upgrade involves shutting down the old MySQL server, replacing the old MySQL binaries or the packages with the new ones.Once this is done, the MySQL server is restarted on the existing data directory.After this, the remaining parts of the existing installation, that require some kind of upgrade, are upgraded.For some Linux platforms, MySQL installation from RPM or Debian ...
Read MoreHow To Check MySQL Version
Let us understand how to check the version of MySQL that the user is currently running −Before entering queries on the console, it is important to ensure that the user is connected to the server.Check MySQL VersionThe below query would give the version number of the server being used, and the current date.mysql> SELECT VERSION(), CURRENT_DATE;Note: The function ‘VERSION()’ and ‘CURRENT_DATE’ are case −insensitive. This means ‘version()’, ‘Version()’, ‘vERsion()’, all mean the same. Same goes with ‘CURRENT_DATE’QueriesLearn about MySQL QueriesAn SQL query is followed by a semi−colon.When a query is issued to mysql, it sends the query to the server ...
Read MoreInstalling MySQL from source on linux
Linux supports many different methods to install MySQL. Only one of the distributions from Oracle needs to be used out of the many installations available.StepsType − Apt, set up method−Enable the MySQL Apt repositoryType − Yum, set up method−Enable the MySQL Yum repositoryType − Zypper, set up method−Enable the MySQL SLES repositoryType − RPM, set up method−Download a specific packageType − DEB, set up method−Download a specific packageType − Generic, set up method−Download a generic packageType − Source, set up method−Compile from sourceType − Docker, set up method−Use Docker Hub for MySQL Community Edition; download Docker image for MySQL Enterprise ...
Read MoreDealing with Problems Compiling MySQL
Some problems with compiling MySQL could be because of not configuring properly. Hence, the solution is to reconfigure.If CMake is run right after it was previously run, there is a possibility that it would use information that was gathered from its previous call. This information is present in CMakeCache.txt. When CMake begins, it looks for this file and reads the contents (if it exists), assuming that the information is correct. This assumption becomes wrong when the file is reconfigured.Each time CMake is run, ‘make’ has to be executed again to recompile. The old object files from previous builds can be ...
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