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Including Comments in SQL Statements in MySQL
How To Include Comments in SQL Statements in MySQL? If you want to include comments in a SQL statement, you can first enter "--", then enter your comment until the end of the line. The tutorial exercise below shows you some good examples: SELECT 'Hello world!' FROM DUAL; -- My first SQL statement! I...
2018-04-12, 659👍, 0💬

Performing Comparison on Character Strings in SQL Server
How To Perform Comparison on Character Strings in SQL Server Transact-SQL? Comparison operations on character strings are performed based on the associated collation. Each collation defines rules on how characters are ordered, how character cases and accents are treated, etc. The tutorial exercise b...
2017-01-21, 659👍, 0💬

Show All Background Sessions in the Database in Oracle
How To Get a List of All Background Sessions in the Database in Oracle? If you don't like to use a SELECT statement to get a list of all background sessions in the current database, you can use the Reports view to do this as shown in the following tutorial example. You need to connect to the server ...
2019-01-26, 658👍, 0💬

Define a Specific RECORD Type in Oracle
How To Define a Specific RECORD Type in Oracle? If you want to define a specific RECORD type, you need to use the TYPE ... IS RECORD statement in the declaration part of any procedure or function. The following example script defines a RECORD type called STUDENT: CREATE OR REPLACE PROCEDURE HELLO AS...
2018-09-01, 658👍, 0💬

Use "IF" Statements with Multiple Conditions in Oracle
How To Use "IF" Statements on Multiple Conditions in Oracle? If you have multiple blocks of codes to be executed based on different conditions, you can use the "IF ... ELSIF" statement. Here is a sample script on IF statements: DECLARE day VARCHAR2; BEGIN day := 'SUNDAY'; IF day = 'THURSDAY' THEN DB...
2018-07-13, 658👍, 0💬

Differences of CHAR and NCHAR in SQL Server Transact-SQL
What Are the Differences between CHAR and NCHAR in SQL Server Transact-SQL? Both CHAR and NCHAR are fixed length data types in Transact-SQL. But they have the following main differences: CHAR stores characters based on the code page with 1 byte per character most of the time. NCHAR stores characters...
2017-04-04, 658👍, 0💬

Rollback the Current Transaction in MySQL
How To Rollback the Current Transaction in MySQL? If you have used some DML statements updated some data objects, you find a problem with those updates, and you don't want those updates to be permanently recorded in the database, you can use the ROLLBACK command. It will remove all the database chan...
2016-10-17, 658👍, 0💬

Create a Table Index in Oracle
How To Create a Table Index in Oracle? If you have a table with a lots of rows, and you know that one of the columns will be used often a search criteria, you can add an index for that column to in improve the search performance. To add an index, you can use the CREATE INDEX statement as shown in th...
2019-05-01, 657👍, 0💬

Rebuild an Index in Oracle
How To Rebuild an Index in Oracle? If you want to rebuild an index, you can use the "ALTER INDEX ... REBUILD statement as shown in the following SQL script: SELECT index_name, table_name, uniqueness FROM USER_INDEXES WHERE table_name = 'EMPLOYEES'; INDEX_NAME TABLE_NAME UNIQUENES -------------------...
2019-04-17, 657👍, 0💬

Define an Explicit Cursor in Oracle
How To Define an Explicit Cursor in Oracle? An explicit cursor must be defined in the declaration part of a procedure or function with the CURSOR ... IS statement as shown in the following sample script: DECLARE CURSOR c_list IS SELECT * FROM countries; CURSOR t_list IS SELECT * FROM employees WHERE...
2018-07-22, 657👍, 0💬

Delete an Existing Column in a Table in MySQL
How To Delete an Existing Column in a Table in MySQL? If you have an existing column in a table and you do not need that column any more, you can delete it with "ALTER TABLE ... DROP COLUMN" statement. Here is a tutorial script to delete an existing column: mysql&gt; ALTER TABLE tip DROP COLUMN ...
2018-03-04, 657👍, 0💬

Sorting Query Output in MySQL
How To Sort the Query Output in MySQL? If you want the returning rows to be sorted, you can specify a sorting expression in the ORDER BY clause. The simplest sort expression is column name who's values will be sorted by. The following select statement returns rows sorted by the values in the "counts...
2017-11-02, 657👍, 0💬

Query with a Right Outer Join in MySQL
How To Write a Query with a Right Outer Join in MySQL? If you want to query from two tables with a right outer join, you can use the RIGHT OUTER JOIN ... ON clause in the FROM clause. The following query returns output with a right outer join from two tables: fyi_links and fyi_rates. The join condit...
2017-09-28, 657👍, 0💬

Creating a Large Table with Random Data for Indexes in SQL Server
How To Create a Large Table with Random Data for Index Testing in SQL Server? If you want to see how index can be used to improve data search performance, you have to build some large tables, which requires large amount of random data. This tutorial exercise helps you to build a large table with pur...
2016-11-13, 657👍, 0💬

"DISABLE TRIGGER" - Disabling Triggers in SQL Server
How To Disable Triggers using "DISABLE TRIGGER" in SQL Server? If want to stop the execution of an existing trigger temporarily, you can use the "DISABLE TRIGGER" statement to disable it. The disabled trigger will be kept in the database. If you want to resume the execution of a disabled trigger, yo...
2016-10-24, 657👍, 0💬

Insert Multiple Rows with 1 INSERT Statement in Oracle
How To Insert Multiple Rows with One INSERT Statement in Oracle? If you want to insert multiple rows with a single INSERT statement, you can use a subquery instead of the VALUES clause. Rows returned from the subquery will be inserted the target table. The following tutorial exercise gives a good ex...
2020-01-29, 656👍, 0💬

Count Duplicated Values in a Column in Oracle
How To Count Duplicated Values in a Column in Oracle? If you have a column with duplicated values, and you want to know what are those duplicated values are and how many duplicates are there for each of those values, you can use the GROUP BY ... HAVING clause as shown in the following example. It re...
2019-11-21, 656👍, 0💬

Categories of Data Types in PL/SQL in Oracle
How Many Categories of Data Types in Oracle? PL/SQL data types are grouped into 4 categories: Scalar Data Types: A scalar data type holds a single value. Composite Data Types: A composite data type has internal components, such as the elements of an array. LOB Data Types: A LOB data type holds a lob...
2018-11-17, 656👍, 0💬

Use Variables in SQL Statements in Oracle
Can Variables Be Used in SQL Statements in Oracle? Yes, you can use variables in SQL statements as part of any expressions. The tutorial script provides you some good examples: (Connect to XE with SQL*Plus) CREATE TABLE student (id NUMBER(5) PRIMARY KEY, first_name VARCHAR(80) NOT NULL, last_name VA...
2018-09-24, 656👍, 0💬

What Are DDL Statements in MySQL
What Are DDL Statements in MySQL? DDL (Data Definition Language) statements are statements to create and manage data objects in the database. The are 3 primary DDL statements: CREATE - Creating a new database object. ALTER - Altering the definition of an existing data object. DROP - Dropping an exis...
2018-03-10, 656👍, 0💬

What Is "mysqlshow" Command in MySQL
What Is "mysqlshow" in MySQL? "mysqlshow" is a command-line interface for end users to see information on tables and columns. Here are some sample commands supported by "mysqlshow": "mysqlshow" - Shows all the databases. "mysqlshow databaseName" - Shows all the tables in the specified database. "mys...
2018-02-28, 656👍, 0💬

Counting Duplicated Values in a Column in MySQL
How To Count Duplicated Values in a Column in MySQL? If you have a column with duplicated values, and you want to know what are those duplicated values are and how many duplicates are there for each of those values, you can use the GROUP BY ... HAVING clause as shown in the following example. It ret...
2017-10-16, 656👍, 0💬

Creating Stored Procedures with Parameters in SQL Server
How To Create Stored Procedures with Parameters in SQL Server Transact-SQL? Very often, you need to create a stored procedure with one or more parameters. You only supply values to those parameters at the time of executing the stored procedure. Stored procedures with parameters can be created with t...
2017-01-05, 656👍, 0💬

OUTPUT - Receiving Output Values from Stored Procedures in SQL Server
How To Receive Output Values from Stored Procedures in SQL Server Transact-SQL? If an output parameter is defined in a stored procedure, the execution statement must provide a variable to receive the output value in the format: "@variable_name OUTPUT" or "@parameter_name = @variable_name OUTPUT". Th...
2016-12-28, 656👍, 0💬

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