MySQL

MySQL

1. Data types

   • https://www.youtube.com/watch?v=7fOdo8PhPaw&list=PL_RGaFnxSHWr_6xTfF2FrIw-NAOo3iWMy&index=7
   • Numeric type
     • BigInt (Really Larger Numebrs)
     • Int (Big Values)
     • Small Int (-32,768 to 32, 767)
     • Tinyint (0 to 255)
     • Decimal (m,d)
     • Numeric (same As Decimal)
     • Float (m,d)
   • Date and Time Data Type
     • Datetime (YYYY-MM-DD HH:MM:SS)
     • Date
       • MySQL - (YYYY-MM-DD) Oracle - (DD-MMM-RR)
       • Question
         • How to See the Format in results ?
     • Time (HH:MM:SS)
     • Year (YYYY)
   • Character Type
     • Char (M)
     • Varchar (M)
     • Text (to store large amount of text)
   • Blob (binary large object) - for storing images
   • Questions
     • Unable to change the Column data type from Numeric to INT in SQL Deveopler tool... Why? Can we change the data type after table is created via SQL commands ??

2. Constraints

   • https://www.youtube.com/watch?v=bIFB-rz315U&index=8&list=PL_RGaFnxSHWr_6xTfF2FrIw-NAOo3iWMy
   • Not Null Constraint
     • If you want to make sure taht a field gets some value for every row in the table, apply the not null constraint to it.
   • Default Constraint
     • If while populating a table you miss giving a colum some value, the default value will be used
   • Unique constraint
     • Unique constraint makes sure that all values entered for the field on which the constraint applied are different
   • Primary Key Constraint
     • Not Null + Unique

3. DDL

   • Create Table
     • Name the Table Define the Columns Mention data types of columns
     • Syntax
       • CREATE TABLE table_name ( col1 datatype, col2 datatype, . . col n datatype, PRIMARY KEY (column));
     • Example
       • CREATE TABLE employee ( id int PRIMARy KEY,  name varchar (50),  dob date,  email VARCHAR(50) ) =============== Create table emp_info as select id, name from employee;
     • Questions
       • 1. How to check the Constraints of a table ? 2. How to see the list of tables in Oracle ? (SHOW Tables - in MySQL) 3. How to check the two tables are having same columns or not ? 4. DB defined column names - like - ROWID in Oracle DB ?
   • Remove Table
     • Deleting a table from database. Make sure to ensure the table by using  1) SHOW TABLES 2) DESC table_name
     • Syntax
       • DELETE TABLE table_name;
     • Questions
       • How to Remove only data from table ? any way to restore the deleted table ?
   • TRUNCATE
     • Syntax
       • TRUNCATE TABLE tab_name

4. DML

   • INSERT
     • https://www.youtube.com/watch?v=Tet3Z7Yb2gg&list=PL_RGaFnxSHWr_6xTfF2FrIw-NAOo3iWMy&index=12
     • Syntax
       • INSERT INTO table_name (Col 1, col3) VALUES (val 1, val 3) ==================== INSERT INTO table_name VALUES (val 1, val 2, .., val n) >> order of the values need to be correct in second one ==================== INSERT INTO emp_info (id,name, dob, email)  select from id, name, dob, email from employee. >> we can insert the data from other table also.
     • Questions
       • Can we avoid the column names, when inserting from another table like -  INSERT INTO emp_info (id,name,dob, email) SELECT all FROM employee;
   • SELECT
     • Syntax
       • SELECT col1, col3,.., coln FROM Table_name
     • WHERE Clause
       • Used to mention the conditions & joining the differnt tables
       • Syntax
         • SELECT col1 FROM table_name [WHERE condition]
     • TOP / LIMIT Clause
       • Used to fect the top N number of records from query. Not all DBs support Oracle supports ROWNUM while MySQL uses LIMIT
       • Syntax
         • MySQL -  SELECT Col-ListFROM table_name[WHERE condition]LIMIT n;
     • ORDER BY Clause
       • Syntax
         • SELECT col-list FROM table_name [WHERE Condition] [ORDER BY Col2,Col4] [ASC/DSC]
     • GROUP BY Clause
       • GROUP BY always follow the WHERE Clause and must precede the ORDER BY clause
       • Syntax
         • SELECT col-list FROM table_name Where Condition [GROUP BY col] [ORDER BY col]
     • DISTINT keyword
       • Used to fetch the single record only, when table is having the same value/data in multiple rows
     • AS Clause
       • Giving different name to column headers in SELECT
   • UPDATE
     • Syntax
       • UPDATE table_name SET col2=val2,..coln=valn [WHERE condition]
   • DELETE
     • Syntax
       • DELETE FROM table_name [WHERE condition]
   • JOINS
     • Syntax
       • SELECT e.ename, d.dname From emp e join DEPT d on e.deptno=d.deptno;
     • Questions
       • Can we use JOINS for update / delete ?
     • LEFT JOIN
     • RIGHT JOIN
     • FULL OUTER JOIN
   • VIEW
     • View is same as a table without any storage.
     • Syntax
       • CREATE VIEW EMP_VIEW AS SELECT EMPNO,ENAME FROM EMP
   • SubQueries

5. Operators

   • These are used with WHERE clause to limit the number of rows in output
   • Arithmetic
     • Addition (+)
     • Subtraction (-)
     • Multiplication (*)
     • Division (/)
     • Modular Division (%)
     • Questions
       • SELECT 5 + 5; is not working in SQL Developers. May be we can't use SQL Developer as calculator ??
   • Comparison
     • To compare data present in columns to data specified in conditions
     • Equal (=)
     • Not Equal (<>)
     • Greater Than (>)
     • Less Than (<)
     • Greather Than or Equal To(>=)
     • Lessthan Or Equal to (<=)
   • Logical
     • ALL
     • AND
     • BETWEEN
     • IN
     • LIKE
       • Used to compare a value to similar values in a table in database Used with Wildcard characters - % (Percentage) &amp; _ (underscore) % - substitution for zero, one or many char's _ - stands for one character or number
       • Syntax
         • SELECT Column-list&nbsp; FROM table_name [WHERE col LIKE '_XXX%']
     • OR
     • IS NULL

6. Functions

   • Map is for MySQL. =========http://www.oracle-dba-online.com/sql/oracle_sql_functions.htm
   • ABS
   • ROUND
   • DIV()
   • MOD()
   • CEIL
   • FLOOR
   • EXP(x)
     • e = 2.57
   • LOG(X)
   • POWER(X,Y)
   • GREATEST(X,Y,Z)
   • LEAST
   • RADIANS
     • Not working in ORACLE SQL
   • SQRT
   • TRUNCATE
   • RAND
   • CONCAT
   • UPPER
   • LOWER
   • INITCAP
   • TRIM
   • SUBSTR
     • select substr('mohammed sami',10,3) from dual; Substr -------- sam
   • RIGHT
   • LEFT
   • LENGTH
   • INSERT
   • REPEAT
   • REPLACE
   • REVERSE
   • STRCMP
   • DATE & TIME
     • ADDDATE
     • SUBDATE
     • DAYNAME
     • CURDATE & CURTIME
     • NOW()
     • MAKEDATE
     • MONTHNAME
     • TIMEDIFF
     • TIME_TO_SEC
   • Aggregate
     • COUNT
     • MAX
     • MIN
     • SUM
     • AVERAGE