SQL and PLSQL » Functions

Oracle CURSOR with parameter

globinch-sql-plsql — Mon, 02 Feb 2009 13:02:00 +0000

Execution of a cursor puts the results of the query into a set of rows called the result set, which can be fetched sequentially or non sequentially.
You can create Cursors which accepts parameters at runtime.

Read:Cursor | Oracle PL/SQL Cursors and example.
Read:ORA-01000: maximum open cursors exceeded.
Read:Oracle Cursors | OPEN ,FETCH and CLOSE Cursor statements.
Read:ORA-01001: invalid cursor

Example:

Step 1:

create table PERSON( PERSON_ID NUMBER(19) not null, AGE       NUMBER(10), FIRSTNAME VARCHAR2(255), LASTNAME  VARCHAR2(255));

SQL> insert into Person values(1,10,'Geek','Greek');

1 row inserted

SQL> insert into Person values(2,12,'Seek','Bells');

1 row inserted

SQL> insert into Person values(3,13,'Creek','Dells');

1 row inserted

SQL>SQL> insert into Person values(4,13,'Sreek','Sells');

1 row inserted

SQL>

Step 2:

Now write a small procedure to illustrate the cursor which accepts a parameter at run time.

create or replace procedure Param_Cursor as

CURSOR PERSON_CUR(pAge NUMBER) isSelect * from Person p where p.age = pAge;

BEGIN    for i in PERSON_CUR(13) loop       dbms_output.put_line(i.firstname);    end loop;

END Param_Cursor;

Step3:

Now run the procedure Param_Cursor.

SQL> set serveroutput on;SQL> exec Param_Cursor;CreekSreek

PL/SQL procedure successfully completed

SQL>

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Oracle: SQL MIN Function | MIN() function in SQL

globinch-sql-plsql — Fri, 09 Jan 2009 10:24:00 +0000

The MIN function returns the minimum value of an expression.MIN() function is reverse of MAX() function.MIN() function can be used along with GROUP BY clause also.

SYNTAX:

SELECT MIN(expression ) FROM tables WHERE (condition);

The example given below explains the usage of MIN() function and usage of MIN along with GROUP BY clause.

SQL> create table MYTABLE (name varchar2(50),age number,department varchar2(20));
Table created

SQL> insert into MYTABLE values ('AAA',12,'D1');
SQL> insert into MYTABLE values ('BBB',42,'D2');
SQL> insert into MYTABLE values ('CCC',22,'D2');
SQL> insert into MYTABLE values ('DDD',32,'D1');

4 row inserted

SQL> select min(age) from MYTABLE;
MIN(AGE)
12

SQL> select min(age) from MYTABLE where age >20;
MIN(AGE)
22

Usage of MIN() function with GROUP BY

SQL> select department ,min(age) from MYTABLE group by department;

DEPARTMENT MIN(AGE)
D1    12<
D2    22

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COUNT() Function in SQL ,Using COUNT(*) and COUNT(1)

globinch-sql-plsql — Fri, 09 Jan 2009 10:18:00 +0000

The COUNT() function returns the number of records in a tables based on sql query.
The COUNT function will only count those records in which the field in the brackets is NOT NULL.

SYNTAX:

SELECT COUNT(expression)
FROM tables
WHERE predicates;

EXAMPLE:
STEP 1:Create the following table,’MYTABLE’ and insert few records.

SQL>  create table MYTABLE (NAME varchar2(50), Age number,id number);
SQL> Table created
SQL> insert into MYTABLE values('BBB',12,1);
SQL> insert into MYTABLE values('DDD',22,2);
SQL> insert into MYTABLE values('CCC',32,3);
SQL> insert into MYTABLE values('AAA',62,4);
SQL> insert into MYTABLE values('CCC',42,5);
SQL>5 rows inserted

STEP 2:Now run the following query.

SQL>  select count(*) from MYTABLE;

COUNT(*)
   5

COUNT function will return the same results regardless of what NOT NULL field(s) you include as the COUNT function parameters
If you use COUNT(*) the query will retrieve all fields from the table inorder to calculate count,To avoid this we can use COUNT(1) instead of COUNT(*).It will merely retrieve the numeric value of 1 for each record that meets your criteria.This can be used as a performance tip.

It is possible to use DISTINCT clause within the COUNT function to give exact count omitting duplicates.

SQL> select count(distinct name) names from mytable;
NAMES
  4
SQL>

You can also use GROUP BY function along with COUNT( Check GROUP BY Here).
This is required when you need a combination of coulmns and number of records in a result set.Because you have listed one column in your SELECT statement that is not encapsulated in the COUNT function, you must use a GROUP BY clause.

EXAMPLE: The following query will give you name and number of occurances from MYTABLE.

SQL>  select name ,COUNT( NAME) from MYTABLE GROUP BY name;

NAME                                               COUNT(NAME)
BBB                                                       1
CCC                                                       2
AAA                                                       1
DDD                                                       1

SQL>

EXAMPLE: The following query will return people with age<40

SQL> select name ,count(*)NUMBER_OF_PEOPLE from mytable where age<40;
NAME                                               NUMBER_OF_PEOPLE
BBB                                                 1
CCC                                                 1
DDD                                                 1

SQL>

EXAMPLE: The following query will return people with age>30

SQL> select name ,count(*)NUMBER_OF_PEOPLE from mytable where age >30 group by name;
NAME                                               NUMBER_OF_PEOPLE
CCC                                                           2
AAA                                                           1
SQL>

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‘ORDER BY’ clause in SQL | Using SQL order by

globinch-sql-plsql — Fri, 09 Jan 2009 10:15:00 +0000

The keyword ‘ORDER BY‘ clause used in SQL to order the data sets retrieved from a SQL database.
The sorting of result set can be based on column or columns.

Example:
Step:1: Create the table as follows:

SQL>  create table MYTABLE (NAME varchar2(50), Age number,id number);<
Table created
SQL>

STEP:2: Insert few records into ‘MYTABLE’.

SQL> insert into MYTABLE values('BBB',22,1);
SQL> insert into MYTABLE values('DDD',22,2);
SQL> insert into MYTABLE values('CCC',22,3);
SQL> insert into MYTABLE values('AAA',22,4);
SQL> insert into MYTABLE values('EEE',22,5);

STEP:3: Run a normal query to retrieve the result set.

SQL>  select * from MYTABLE;
NAME                                                     AGE         ID
BBB                                                        22          1<
DDD                                                        22          2
CCC                                                        22          3
AAA                                                        22          4
EEE                                                        22          5

STEP:4: Now use the ‘ORDER BY‘ keyword in the query and use ‘NAME’ column to sort.

SQL>  select * from MYTABLE order by name;
NAME                                                      AGE         ID
AAA                                                        22          4
BBB                                                        22          1
CCC                                                        22          3
DDD                                                        22          2
EEE                                                        22          5

By defaults the ‘ORDER BY‘ query returns natural ordered results.Otherwise you need to use ‘ASC‘ or ‘DESC‘ keywords.
ORDER BY clause usually followed by ‘ASC‘ or ‘DESC‘ keywords in order to indicate the sorting order either by ‘ascending’ or ‘descending’.
ASC keyword orders the result set by the specified columns alphabetically. DESC sort the result set backwards ,i.e just opposite of ‘ASC’

STEP:5: Use the ‘DESC‘ keyword in the query mentioned in STEP:4

SQL> select * from MYTABLE order by name DESC;
NAME                                                      AGE         ID
EEE                                                        22          5
DDD                                                        22          2
CCC                                                        22          3
BBB                                                        22          1
AAA                                                        22          4

You can sort your result set by more than one column by specifying those columns in the SQL ORDER BY list.When using ORDER BY with more than one column, you need to separate the columns following ORDER BY with commas.
If you need specific ordering based on more than one column, you need to specify ASC and/or DESC after each column.

STEP:6: Example of using multiple columns in ‘ORDER BY’ clause.

SQL>  select * from MYTABLE order by name ASC,ID DESC;
NAME                                                      AGE         ID
AAA                                                        22          4
BBB                                                        22          1
CCC                                                        22          3
DDD                                                        22          2
EEE                                                        22          5

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Oracle Max(Date) function usage-SQL max date

globinch-sql-plsql — Thu, 04 Dec 2008 12:31:00 +0000

Max() function in sql can be used to get maximum value of two or more dates.Max(Date) function is useful in retrieving the maximum value of date from a record set or column or result set etc.The following examples shows the usage of Max() function to find out maximum value of dates.

Read more about SQL MAX() function here.
Read more about oracle DATE here >> DATE Data type,TO_DATE ,TO_CHAR ,TO_TIMESTAMP,timestamp format,DATE vs TIMESTAMP ,comparing dates,DATE Format

Example for Max(date):

Step 1: Create table DATETABLE as follows ,which is having a DATE column as ‘thedate’.

SQL>  create table DateTable (id number, thedate date);
Table created

STEP 2: Insert the following records in DATETABLE.

SQL> insert into dateTable values(1, sysdate-1);
SQL> insert into dateTable values(2, sysdate);
SQL> insert into dateTable values(3, sysdate+1);
SQL> insert into dateTable values(4, sysdate+2);

4 row inserted

STEP 3: Query the table for Id of the row which is having the maximum value of ‘thedate’.

SQL>  select id from datetable where thedate =(select max(thedate) from datetable);
ID
4

Read more about SQL MAX() function here.
Read more about oracle DATE here >> DATE Data type,TO_DATE ,TO_CHAR ,TO_TIMESTAMP,timestamp format,DATE vs TIMESTAMP ,comparing dates,DATE Format

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Oracle Trim Function | PL/SQL TRIM() Function.

globinch-sql-plsql — Thu, 04 Dec 2008 11:15:00 +0000

See Other related SQL and PLSQL Functions :
>>> DECODE ,MAX ,NVL ,INSTR ,SUBSTR ,TO_DATE ,TO_CHAR ,TO_TIMESTAMP ,GROUP BY,Extract

TRIM function removes all specified characters from the beginning of a string or from the ending of a string.

Syntax:

trim( [ leading or trailing or both  , trim_string ,   stringToTrim )

leading - This removes the ‘trim_string‘ from the beginning of ‘stringToTrim‘.
trailing -This removes the ‘trim_string‘ from the end of ‘stringToTrim‘.
both - This removes the ‘trim_string‘ from the front and end of ‘stringToTrim‘.

By default if there is no choice give oracle will remove ‘trim_string‘ from the front and end of ‘stringToTrim‘.

Examples:

1. Default Options

SQL> select trim ('  abcd ') from dual;

TRIM('ABCD')
abcd
SQL>

2. Option ‘trailing’ Example.

SQL> select trim(trailing 'C' from 'ABC') from dual;

TRIM(TRAILING'C'FROM'ABC')
AB
SQL>

3. Option ‘leading’ Example.

 select trim(leading 'A' from 'ABC') from dual;
TRIM(LEADING'A'FROM'ABC')
BC

4. Option ‘both’ Example

SQL> select trim(both 'A' from 'ABCA') from dual;
TRIM(BOTH'A'FROM'ABCA')
BC

5. Another example for option ‘both’.

SQL> select trim(both 'A' from 'AAAAABCAAAAAAAAA') from dual;
TRIM(BOTH'A'FROM'AAAAABCAAAAAA
BC

Other Functions :>>> DECODE ,MAX ,NVL ,INSTR ,SUBSTR ,TO_DATE ,TO_CHAR ,TO_TIMESTAMP ,GROUP BY,Extract

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Oracle Decode Function | Use PLSQL DECODE function to handle NULL and default values

globinch-sql-plsql — Wed, 03 Dec 2008 11:34:00 +0000

The DECODE function works as multiple if conditions or CASE statements.
The DECODE function compares one expression to one or more expressions and returns the corresponding result expression.The default value will be returned when there is no match.It allows to transform data values at run time.

In newer versions of Oracle the CASE is used instead of DECODE.

Syntax:

decode( expression , search_1 , result_value1 ,...., search_n , result_valuen , default_value )

At the end of the decode statement is the default value

Example:

Step1: Create a table and insert records as follows

SQL> create table marks(name varchar2(20),grade number,mark number);

Table created

SQL> insert into  marks values ('Chris',1,6);
SQL> insert into  marks values ('James',3,4);
SQL> insert into  marks values ('John',2,5);
SQL> insert into  marks values ('Ram',1,6);
SQL> insert into marks values('Kate', 4,3);

5 rows inserted.

Now let us get the details and based on the number value of the Grade let us get the detailed values.

SQL> select name,mark ,decode(grade,1,'GRADE A',2,'GRADE B',3,'GRADE C', 'Below Average') Grade from marks;
NAME                           MARK     GRADE
Chris                             6     GRADE A
James                             4     GRADE C
John                              4     GRADE B
Ram                               6     GRADE A

In the above example we use the DECODE function to check the grade value and display the Grades in textual form.There is a default value ‘Below Average’ when grades are not 1,2 or 3.

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SQL: MAX Function | Oracle Max() examples

globinch-sql-plsql — Wed, 03 Dec 2008 06:37:00 +0000

The Max() function is another much helpful function in SQL, the MAX function returns the maximum value of an expression. Read MIN() function here.

Syntax:

SELECT MAX(expression ) FROM tables WHERE ?;

Examples: (See more example for Using MAX() function along with GROUP BY statement here. )

Step 1: Create a table ‘MyTable’ as below.

SQL> create table MyTable (name varchar2(100),address varchar2(500),id number);
Table created
SQL>

Step 2: Insert few rows to ‘MyTable’.

SQL> insert into  mytable values ('name1','msg1',1);
1 row inserted
SQL> insert into  mytable values ('name2','msg2',2);
1 row inserted
SQL> insert into  mytable values ('name3','msg3',3);
1 row inserted
SQL>

Step 3: Now let us select the maximum ‘id’ from ‘Mytable’.

SQL> select max(id) from mytable;
MAX(ID)
3

Step 4: Now let us retrive the complete row with maximum values of ‘id’;

SQL> select * from mytable where id = (select max(id) from mytable);
NAME                     MSG                     ID
name3                    msg3                     3<
SQL>

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SQL GROUP BY Statement | Oracle GROUP BY Clause examples

globinch-sql-plsql — Wed, 03 Dec 2008 06:30:00 +0000

The GROUP BY statement is used in conjunction with the aggregate functions like SUM to provide means of grouping the result by certain table column or columns.

Syntax:

SQL> SELECT columnName, aggregate_function(columnName)
FROM tableName
WHERE
GROUP BY columnName

Examples :

Step 1: Create a table ‘MyTable’ as below.

SQL> create table MyTable (name varchar2(100),address varchar2(500),marks number);

Table created

Step 2: Insert few rows to ‘MyTable’.

SQL> insert into  mytable values ('Chris','Add1',1);
SQL> insert into  mytable values ('John','Add2',2);
SQL> insert into  mytable values ('John','Add2',3);
SQL> insert into  mytable values ('John','Add2',4);
SQL> insert into  mytable values ('Chris','Add1',5);
5 rows inserted

Step 3: Now let us calculate the total marks for Chris and John using GROUP BY Clause.

SQL> select name,SUM(marks) from mytable GROUP BY name;
NAME                                         SUM(MARKS)
John                                                        9
Chris                                                       6

NVL | Oracle/PLSQL: NVL Function

globinch-sql-plsql — Mon, 01 Dec 2008 07:55:00 +0000

NVL function is used to substitute a value when a null value is encountered.This is useful in PL/SQL programming where we can supply default values when there is a chance of getting null at run time or to provide useful logging messages.

Example is given below.

SQL> set serveroutput on;
SQL> -- Created on 12/1/2008 by PLSQLTech Tips
SQL> declare
-- Local variables here
myStr varchar2(100);
begin
--Initialize the String
myStr := 'This is my string';
dbms_output.put_line(nvl(myStr,'This is to replace if string is null'));
--Now set the String to null;
myStr := null;
dbms_output.put_line(nvl(myStr,'This is to replace if string is null'));
end;
/

This is my string
This is to replace if string is null
PL/SQL procedure successfully completed.
SQL>

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