Sql Statements are used to retrieve data from the database. We can get same results by writing different sql queries. But use of the best query is important when performance is considered. So you need to sql query tuning based on the requirement. Here is the list of queries which we use reqularly and how these sql queries can be optimized for better performance.
SQL Tuning/SQL Optimization Techniques:1) The sql query becomes faster if you use the actual columns names in SELECT statement instead of than...
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Tuesday, 17 April 2012
Oracle Functions
There are two types of functions in Oracle.
1) Single Row Functions: Single row or Scalar functions return a value for every row that is processed in a query.
2) Group Functions: These functions group the rows of data based on the values returned by the query. This is discussed in SQL GROUP Functions. The group functions are used to calculate aggregate values like total or average, which return just one total or one average value after processing a group of rows.
There are four types of single row functions. They are:
1) Numeric Functions:...
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Oracle Functions
SQL GRANT and REVOKE
DCL commands are used to enforce database security in a multiple user database environment. Two types of DCL commands are GRANT and REVOTE. Only Database Administrator's or owner's of the database object can provide/remove privileges on a databse object.
SQL GRANT CommandSQL GRANT is a command used to provide access or privileges on the database objects to the users.
The Syntax for the GRANT command is:
GRANT privilege_name
ON object_name
TO {user_name |PUBLIC |role_name}
[WITH GRANT OPTION];
privilege_name is the access right or...
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SQL GRANT and REVOKE
SQL Index
Index in sql is created on existing tables to retrieve the rows quickly.
When there are thousands of records in a table, retrieving information will take a long time. Therefore indexes are created on columns which are accessed frequently, so that the information can be retrieved quickly. Indexes can be created on a single column or a group of columns. When a index is created, it first sorts the data and then it assigns a ROWID for each row.
Syntax to create Index:
CREATE INDEX index_name
ON table_name (column_name1,column_name2...);
Syntax...
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SQL Index
SQL Subquery
Subquery or Inner query or Nested query is a query in a query. A subquery is usually added in the WHERE Clause of the sql statement. Most of the time, a subquery is used when you know how to search for a value using a SELECT statement, but do not know the exact value.
Subqueries are an alternate way of returning data from multiple tables.
Subqueries can be used with the following sql statements along with the comparision operators like =, <, >, >=, <= etc.
SELECT
INSERT
UPDATE
DELETE
For Example:
1) Usually, a subquery should...
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SQL Subquery
SQL Views
A VIEW is a virtual table, through which a selective portion of the data from one or more tables can be seen. Views do not contain data of their own. They are used to restrict access to the database or to hide data complexity. A view is stored as a SELECT statement in the database. DML operations on a view like INSERT, UPDATE, DELETE affects the data in the original table upon which the view is based.
The Syntax to create a sql view is
CREATE VIEW view_name
AS
SELECT column_list
FROM table_name [WHERE condition];
view_name is the name...
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SQL Views
SQL JOINS
SQL Joins are used to relate information in different tables. A Join condition is a part of the sql query that retrieves rows from two or more tables. A SQL Join condition is used in the SQL WHERE Clause of select, update, delete statements. The Syntax for joining two tables is:
SELECT col1, col2, col3...
FROM table_name1, table_name2
WHERE table_name1.col2 = table_name2.col1;
If a sql join condition is omitted or if it is invalid the join operation will result in a Cartesian product. The Cartesian product returns a number of rows...
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SQL JOINS
