Limit dan Offset rows

Hai semuanya, di materi kali ini kita akan membahas tentang Limit dan Offset. Seperti biasa materinya kita akan bagi-bagi seperti berikut:

1. Limit clause
2. Offset clause
3. Applying limit and offset together

Ok langsung aja kita bahas materi yang pertama:

Limit clause

Dengan LIMIT clause kita bisa membatasi data yang akan di tampilkan dari hasil yang di proses oleh query. Secara konsep fungsi limit jika kita gambarkan seperti berikut:

Penggunaan limit di PostgreSQL ada 2 cara yaitu dengan memberikan count row atau number dan menggunakan keyword ALL. If a limit count is given, no more than that many rows will be returned (but possibly fewer, if the query itself yields fewer rows). LIMIT ALL is the same as omitting the LIMIT clause, as is LIMIT with a NULL argument.

Basic format Limit clause seperti berikut:

SELECT select_list
FROM table_expression
[ ORDER BY ... ]
[ LIMIT { number | ALL } ]

When using LIMIT, it is important to use an ORDER BY clause that constrains the result rows into a unique order. Otherwise you will get an unpredictable subset of the query’s rows.

Contoh penggunaannya seperti berikut:

Jika dijalankan maka hasilnya seperti berikut:

hr=# select employee_id, first_name, salary, commission_pct
hr-# from employees
hr-# order by employee_id
hr-# limit 10;
 employee_id | first_name |  salary  | commission_pct
-------------+------------+----------+----------------
         100 | Steven     | 24000.00 |
         101 | Neena      | 17000.00 |
         102 | Lex        | 17000.00 |
         103 | Alexander  |  9000.00 |
         104 | Bruce      |  6000.00 |
         105 | David      |  4800.00 |
         106 | Valli      |  4800.00 |
         107 | Diana      |  4200.00 |
         108 | Nancy      | 12000.00 |
         109 | Daniel     |  9000.00 |
(10 rows)

Offset clause

OFFSET says to skip that many rows before beginning to return rows. OFFSET 0 is the same as omitting the OFFSET clause, as is OFFSET with a NULL argument. Secara konsep fungsi OFFSET jika kita gambarkan seperti berikut:

Basic format offset clause seperti berikut:

SELECT select_list
FROM table_expression
[ ORDER BY ... ]
[ OFFSET number ]

Sama halnya dengan LIMIT, kita membutuhkan ORDER BY clause untuk mendapatkan data yang predicatable.

Contoh penggunaannya seperti berikut:

Jika dijalankan maka hasilnya seperti berikut:

hr=# select employee_id, first_name, salary, commission_pct
hr-# from employees
hr-# order by employee_id
hr-# offset 100;
 employee_id | first_name |  salary  | commission_pct
-------------+------------+----------+----------------
         200 | Jennifer   |  4400.00 |
         201 | Michael    | 13000.00 |
         202 | Pat        |  6000.00 |
         203 | Susan      |  6500.00 |
         204 | Hermann    | 10000.00 |
         205 | Shelley    | 12000.00 |
         206 | William    |  8300.00 |
(7 rows)

Applying limit and offset together

If both OFFSET and LIMIT appear, then OFFSET rows are skipped before starting to count the LIMIT rows that are returned. Secara konsep fungsi LIMIT dan OFFSET jika kita gabungkan maka ilustrasinya seperti berikut:

SQL Format limit & offset clause seperti berikut:

SELECT select_list
FROM table_expression
[ ORDER BY ... ]
[ LIMIT { number | ALL } ] 
[ OFFSET number ]

Contoh penggunaannya seperti berikut:

Jika dijalankan maka hasilnya seperti berikut:

hr=# select employee_id, first_name, salary, commission_pct
hr-# from employees
hr-# order by employee_id
hr-# limit 5
hr-# offset 100;
 employee_id | first_name |  salary  | commission_pct
-------------+------------+----------+----------------
         200 | Jennifer   |  4400.00 |
         201 | Michael    | 13000.00 |
         202 | Pat        |  6000.00 |
         203 | Susan      |  6500.00 |
         204 | Hermann    | 10000.00 |
(5 rows)

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