v 1.0 oe nik 2013 1 dbman 2 sql introduction select basics select suffixes: from, order by, where

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SQL IntroductionSelect basicsSelect suffixes: FROM, ORDER BY, WHERE

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Introduction

• SQL = Structured Query Language• From the ’70s: IBM, first user: Oracle• Standards: SQL-86, SQL-89, SQL-92, SQL:1999,

SQL:2003, SQL:2008• CREATE, ALTER• SELECT• UPDATE, DELETE• Various prefixes, suffixes; different approaches;

different function names/parameters „SQL Dialects”

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SQL Servers

• Oracle, IBM (DB2), Microsoft (MSSQL), Sybase (ASE, SQLAnywhere), Teradata

• PostgreSQL (~ Sun), MySQL ( Sun), Firebird, Interbase, MSACCESS

• Operating System: Oracle: Linux, Sun: Unix (Solaris), Microsoft: Windows Server, IBM: Unix (AIX)

• Development environments: Sun: Java, Microsoft: .NET, [Others: external libraries]

• Hardware: Sun: Sparc + Server/Workstation/ Storage, IBM: Datacenter, Server

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20th of April, 2009.

• The contract is signed that means that Oracle buys the whole Sun Microsystems

• PostgreSQL, MySQL ( Sun), Firebird, Interbase, MSACCESS

• Operating Systems: Oracle: Linux, Sun: Unix (Solaris), Microsoft: Windows Server, IBM: Unix (AIX)

• Development environments: Sun: Java, Microsoft: .NET, [Others: external libraries]

• Hardware: Sun: Sparc + Server/Workstation/ Storage, IBM: Datacenter, Server

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• „Oracle Corporation (NASDAQ:ORCL) announced today that it had completed its acquisition of Sun Microsystems, Inc.”

• „This time, the difficulty was persuading European antitrust regulators who were concerned about the fate under Oracle of the open-source MySQL database software business that was part of Sun.”

• „With the addition of servers, storage, Sparc processors, the Solaris operating system, Java, and the MySQL database to Oracle's portfolio of database, middleware, and business applications, we plan to engineer and deliver open and integrated systems -- from applications to disk -- where all the pieces fit and work together out of the box.”

• www.sun.com www.oracle.com/sun/

27th of January, 2010.

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Sun?• OpenSolaris: KO ( OpenIndiana)• MySql: „alive?” ( MariaDB: LAMP, Google, Mozilla,

Wikimedia … Arch, Fedora, Gentoo, OpenSUSE, RedHat, Slackware)

• OpenOffice: KO ( LibreOffice, ApacheOO)• License changes, support changes ( obligatory HW

support) Oracle is an evil (? Cisco, MS ?), but important (!) company The presentations will focus on the Oracle and the MySQL

dialect – we will work with the ORACLE dialectWe will use the Oracle demo tables

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Data Types(Oracle)• These types are used for all columns and function

parameters• Data types:

– char(N) – varchar(N) – varchar2(N) [255byte / 4K]– blob (vs. clob, ~2-4GB)– numeric(N[, M]) / number(N[, M]) / int, float– date / timestamp (time – not available in Oracle

instead usable: interval) alter session set NLS_DATE_FORMAT = 'YYYY-

MM-DD';

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Data Types(MySQL)• char(N) – varchar(N) [rowsize: 65K]• blob (vs. text: tinytext, text, mediumtext, longtext,

max. 4GB)• tinyint (sbyte), smallint (integer), int, bigint (long),

float, double• date / time / datetime / timestamp• Others (year, enum, set, binary, bit, decimal,

numeric, bool – we will not use those)

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Table structure diagram

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Most simple queries

• MySQL:– From phpmyadmin or the command-line client– user: root, pw: empty; tables emp+dept– ora_MY_INIT.sql : import OR source \path\to\x.sql– show databases; use orademo; show tables;

• Oracle– From your browser or from the start menu

(command line)– work1 : magyar : Tigris-1– SQL Scripts / SQL Commands

• select ename from emp; • select * from emp; select * from dept;

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SELECT• Select, order, filter, group the records the swiss

army knife of RDBMS systems

SELECT [prefixes: distinct, into, top, start at]

column1, …, columnN

FROMtable1, ...,tableN

[other suffixes: where, group by, having, union/minus/intersect, order by, limit, offset]

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SELECTProcessing order of suffixes

1. FROM2. WHERE3. GROUP BY4. HAVING5. UNION/MINUS6. INTERSECT7. ORDER BY8. INTO

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SELECTDisplayed order of suffixes

1. INTO2. FROM3. WHERE4. GROUP BY5. HAVING6. UNION/MINUS7. INTERSECT8. ORDER BY

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Using aliases• Table-alias: obligatory for the whole query, the new

name must be used• Field-alias: Only formats/renames the output, the

original name/expression must be used in all suffixes (exception: ORDER BY)

• Oracle: “ for names, ‘ for strings• MSSQL: [] for names, ‘ for strings (possibly “)• MySQL: ` for names, ‘ or “ for strings• select `empno` as ID, ename as "Name", job as ′Job

name′, sal as Salary from emp as Worker;• Name (and alias) SHOULD NOT contain special

letters no need for [“`quoting`”] names!

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Definition of stringsmysql> SELECT 'This\nIs\nFour\nLines';

+--------------------+

| This

Is

Four

Lines |

+--------------------+

mysql> SELECT 'disappearing\ backslash';

+------------------------+

| disappearing backslash |

+------------------------+

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Table alias• select * from emp workers;• select * from dept departments;• select empno from emp;• select emp.empno from emp;• select workers.empno from emp workers;

It will be essential if the same table is used more than once (e.g. worker + boss)

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ORDER BY• select empno, ename from emp order by ename;• select empno, ename from emp order by ename asc; • select empno, ename as NAME from emp order by name

desc;• select ename, sal from emp order by sal asc, ename

desc;

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DISTINCTFilter out repeated output lines:• select mgr from emp order by mgr;• select distinct mgr from emp order by mgr;• select mgr, sal from emp order by mgr;• select distinct mgr, sal from emp order by mgr;

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WHEREOperators

=, <, >, <=, >=, <>• select ename, sal from emp where sal>2000;Between• select ename, sal, comm from emp where sal

between 1000 and 2000;

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WHERENull

• PASCAL: FALSE, 0, ""; ANSI C: 0 == ""• PHP: FALSE == 0 == ""; 0 === "" false• SQL: FALSE, unknown, 0, "", NULL• If there is NOTHING in the field, then it contains NULL• Every operation with NULL results in unknown/NULL

Three-valued-logic avoid! (see later)• select * from emp where comm is null;• select * from emp where comm is not null;

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WHEREOperators

IN, ANY, ALL (non-subquery usage)• select ename, sal, comm from emp

where sal IN (3000, 5000);• select ename, sal, comm from emp

where sal < ANY (3000, 5000);• select ename, sal, comm from emp

where sal < ALL (3000, 5000);• select ename, sal, comm from emp

where comm in (NULL, 500); ???

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WHERELike operator

Like: Comparison string: %=string, _=1 character• select ename, sal from emp where ename like '%E%'; --

upper, lower• select ename, sal from emp where ename like '%E_';• select ename, sal from emp where (sal>2000) and

(ename like '%E%');• select ename from emp where ename like '%\_%'

escape '\';

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Field list – not always with fields onlyConstans, expressions, functions, variables:• select ename, ':' as colon, sal from emp;• select sal, sal+1000 as bigsal from emp;• Oracle> select ename, sysdate, sal from emp;• MySQL> select ename, NOW(), SYSDATE(), CURDATE(),

sal from emp;• Oracle> select ename||' - '||hiredate||' -- '||

sysdate||'.' as FULL from emp;• MySQL> select concat(ename, ' ', '\'s job is', ' ', job) as

full from emp;

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Expressions in the field list

• select ename as Name, sal as Salary from emp;• select ename as Name, (sal+1000) as Salary from emp;• select ename as Name, sal as Salary, comm as Extra,

(sal+comm) as SumSal from emp;

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Treating NULL values

• Oracle, Postgre, MSSQL: NVL, NVL2, Coalesce• MSSQL: ISNULL(p1, p2)• MySQL: Coalesce(p1, p2, p3, …)

IFNULL (p1, p2)• select ename as Name , sal as Salary, comm as Extra,

(sal+ifnull(comm, 0)) as SumSal from emp;• select ename as Name , sal as Salary, comm as Extra,

(sal+ifnull(comm, 0)) as SumSal, ifnull(mgr, 'NONE') as Boss from emp; -- type assignment with oralce+NVL, this can be a problem

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Control flow functions

http://psoug.org/reference/decode_case.html

http://dev.mysql.com/doc/refman/5.0/en/control-flow-functions.html

CASE, if(), ifnull()

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String functions

http://psoug.org/reference/string_func.html , + INSTR, SUBSTR, NVL

http://dev.mysql.com/doc/refman/5.0/en/string-functions.html

• concat_ws(), concat(), instr(), length(), LIKE, lower()/upper(), lpad()/rpad(), ltrim()/rtrim()/trim(), replace(), strcmp(), substr()/substring()

• Row-level functions: select length(ename) as NameLength from emp;

• select ename, rpad('', round(sal/500)+1, '*') as graph from emp;

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Numeric functions

http://psoug.org/reference/number_func.html ABS, COALESCE, LENGTH, MOD, NVL, POWER, ROUND, SQRT, TRUNC+ conversion functions

http://dev.mysql.com/doc/refman/5.0/en/numeric-functions.html

• abs(), ceil()/floor()/round(), conv(), mod(), pow(), rand(), sign(), sqrt()

• Operators: http://dev.mysql.com/doc/refman/5.0/en/arithmetic-functions.html

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Date functionshttp://psoug.org/reference/date_func.html

SYSDATE, TO_CHAR, TO_DATE• alter session set NLS_DATE_FORMAT = 'YYYY-MM-DD'• select hiredate,(to_char(sysdate, 'YYYY')-

to_char(hiredate, 'YYYY')) as diff from emp;• select hiredate,months_between(sysdate, hiredate)/12

from emp;

http://dev.mysql.com/doc/refman/5.0/en/date-and-time-functions.html

• curdate(), date_format(), datediff(), extract(), now(), sysdate(), timediff(), unix_timestamp()

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Date functions• select ename, extract(year from curdate()) - extract(year

from hiredate) as diff from emp;• MySQL> select ename, substr(curdate(), 1, 4) -

substr(hiredate, 1, 4) as diff from emp;• MySQL> select ename, round(datediff(curdate(),

hiredate)/365.25) as diff from emp;• MySQL> select ename,

round( (unix_timestamp(curdate()) - unix_timestamp(hiredate))/86400/365.25) as diff from emp;

• ORACLE> months_between()• MSSQL> datepart()

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SELECTDisplayed order of suffixes

1. INTO2. FROM3. WHERE4. GROUP BY5. HAVING6. UNION/MINUS7. INTERSECT8. ORDER BY

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v 1.0 oe nik 2013 1 dbman 2 sql introduction select basics select suffixes: from, order by, where

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