THIS TOPIC APPLIES TO SQL Server starting with 2008 Azure SQL Database Azure SQL Data Warehouse Parallel Data Warehouse.The SQL Server Database Engine processes.SQL FAQ Oracle FAQOracle SQL FAQ.What is SQL and where does it come fromeditStructured Query Language SQL is a language that provides an interface to relational database systems.The proper pronunciation of SQL, and the preferred pronunciation within Oracle Corp, is sequel and not ess cue ell.SQL was developed by IBM in the 1.Update Date And Time Sql Query Contains' title='Update Date And Time Sql Query Contains' />System R, and is a de facto standard, as well as an ISO and ANSI standard.In common usage SQL also encompasses DML Data Manipulation Language, for INSERTs, UPDATEs, DELETEs and DDL Data Definition Language, used for creating and modifying tables and other database structures.The development of SQL is governed by standards.A major revision to the SQL standard was completed in 1.SQL2.SQL3 support object extensions and are partially implemented in Oracle.Example SQL statements.CREATE TABLE table.NUMBER, column.VARCHAR23. How To Install Sp2 Without Validation Letter .INSERT INTO table.VALUES 1, XYZ.SELECT FROM table.WHERE column.XYZ.What are the difference between DDL, DML and DCL commandseditDDL Data Definition Language statements used to define the database structure or schema.SQLdevDOC/E39885_01/appdev.40/e38414/img/sql_worksheet.gif' alt='Update Date And Time Sql Query Contains' title='Update Date And Time Sql Query Contains' />Craig S.Mullins Database Performance Management Return to Home Page.October 2004 Using Dynamic SQL for Maximum Flexibility.SQL Date Functions Learn SQL Structured Programming Language in simple and easy steps starting from basic to advanced concepts with examples including database.Some examples.CREATE to create objects in the database ALTER alters the structure of the database DROP delete objects from the database TRUNCATE remove all records from a table, including all spaces allocated for the records are removed COMMENT add comments to the data dictionary RENAME rename an object.DML Data Manipulation Language statements used for managing data within schema objects.Some examples.SELECT retrieve data from the a database INSERT insert data into a table UPDATE updates existing data within a table DELETE deletes all records from a table, the space for the records remain MERGE UPSERT operation insert or update CALL call a PLSQL or Java subprogram EXPLAIN PLAN explain access path to the data LOCK TABLE controls concurrency.DCL Data Control Language.Some examples.GRANT gives users access privileges to database REVOKE withdraw access privileges given with the GRANT command.TCL Transaction Control statements used to manage the changes made by DML statements.It allows statements to be grouped together into logical transactions.COMMIT save work done SAVEPOINT identify a point in a transaction to which you can later roll back ROLLBACK undo the modification I made since the last COMMIT SET TRANSACTION Change transaction options like isolation level and what rollback segment to use SET ROLE set the current active roles.DML are not auto commit.DDL are auto commit.Difference between TRUNCATE, DELETE and DROP commandseditThe DELETE command is used to remove some or all rows from a table.A WHERE clause can be used to only remove some rows.If no WHERE condition is specified, all rows will be removed.After performing a DELETE operation you need to COMMIT or ROLLBACK the transaction to make the change permanent or to undo it.Note that this operation will cause all DELETE triggers on the table to fire.SQL SELECT COUNT FROM emp.SQL DELETE FROM emp WHERE job CLERK.SQL COMMIT.Commit complete.SQL SELECT COUNT FROM emp.TRUNCATE removes all rows from a table.The operation cannot be rolled back and no triggers will be fired.As such, TRUNCATE is faster and doesnt use as much undo space as a DELETE.SQL TRUNCATE TABLE emp.Table truncated.SQL SELECT COUNT FROM emp.The DROP command removes a table from the database.All the tables rows, indexes and privileges will also be removed.No DML triggers will be fired.The operation cannot be rolled back.SQL DROP TABLE emp.SQL SELECT FROM emp.SELECT FROM emp.ERROR at line 1.ORA 0.DROP and TRUNCATE are DDL commands, whereas DELETE is a DML command.Therefore DELETE operations can be rolled back undone, while DROP and TRUNCATE operations cannot be rolled back.From Oracle 1. Gta Vice City Camera Hack Modern . Example. SQL FLASHBACK TABLE emp TO BEFORE DROP.Flashback complete.PS DELETE will not free up used space within a table.This means that repeated DELETE commands will severely fragment the table and queries will have to navigate this free space in order to retrieve rows.How does one escape special characters when writing SQL querieseditEscape quotes.Use two quotes for every one displayed.Examples.SQL SELECT Franks Oracle site AS text FROM DUAL.Frankss Oracle site.SQL SELECT A quoted word.AS text FROM DUAL.A quoted word.SQL SELECT A double quoted word.AS text FROM DUAL.A double quoted word.Use Q expression.SQL SELECT qFranks Oracle site AS text FROM DUAL.Franks Oracle site.SQL SELECT qA quoted word.AS text FROM DUAL.A quoted word.SQL SELECT qA double quoted word.AS text FROM DUAL.A double quoted word.Escape wildcard characters.The LIKE keyword allows for string searches.The wild card character is used to match exactly one character, while is used to match zero or more occurrences of any characters.These characters can be escaped in SQL.Examples.SELECT name FROM emp.WHERE id LIKE ESCAPE.SELECT name FROM emp.WHERE id LIKE ESCAPE.Escape ampersand characters in SQLlus.When using SQLlus, the DEFINE setting can be changed to allow s ampersands to be used in text.SELECT Laurel Hardy FROM dual.Other methods Define an escape character.SELECT abc FROM dual.Dont scan for substitution variables.SELECT ABC x FROM dual.Another way to escape the would be to use concatenation, which would not require any SET commands.SELECT Laurel Hardy FROM dual.Use the 1.Quoting mechanism.QUOTECHARTextQUOTECHAR.Make sure that the QUOTECHAR followed by an doesnt exist in the text.SELECT qThis is Orafaqs quoted text field FROM DUAL.Can one select a random collection of rows from a tableeditThe following methods can be used to select a random collection of rows from a table.The SAMPLE Clause.From Oracle 8i, the easiest way to randomly select rows from a table is to use the SAMPLE clause with a SELECT statement.Examples.SELECT FROM emp SAMPLE1.In the above example, Oracle is instructed to randomly return 1.SELECT FROM emp SAMPLE5 BLOCKS.This example will sample 5 of all formatted database blocks instead of rows.This clause only works for single table queries on local tables.If you include the SAMPLE clause within a multi table or remote query, you will get a parse error or ORA 3.SAMPLE option not allowed in statement with multiple table references.One way around this is to create an inline view on the driving table of the query with the SAMPLE clause.Example.SELECT t.FROM SELECT FROM dept SAMPLE5 t.WHERE t.If you examine the execution plan of a Sample Table Scan, you should see a step like this.TABLE ACCESS SAMPLE OF EMP TABLE.ORDER BY dbmsrandom.This method orders the data by a random column number.Example.SQL SELECT FROM SELECT ename.FROM emp.ORDER BY dbmsrandom.WHERE rownum lt 3.The ORAHASH function.The following example retrieves a subset of the data in the emp table by specifying 3 buckets 0 to 2 and then returning the data from bucket 1.SELECT FROM emp WHERE ORAHASHempno, 2 1.How does one eliminate duplicates rows from a tableeditChoose one of the following queries to identify or remove duplicate rows from a table leaving only unique records in the table.Method 1 Delete all rowids that is BIGGER than the SMALLEST rowid value for a given key.SQL DELETE FROM tablename A.WHERE ROWID SELECT minrowid.FROM tablename B.WHERE A.B.Method 2 This method is usually faster.However, remember to recreate all indexes, constraints, triggers, etc.SQL create table tablename.SQL drop table tablename.SQL rename tablename.Method 3 SQL DELETE FROM mytable t.WHERE EXISTS SELECT x FROM mytable t.WHERE t.AND t. 2. keyvalue.AND t.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |