What is the PostgreSQL equivalent of Oracle's ROWNUM and ROWID?

Question

Vinod Chelladurai · Accepted Answer

I have worked with both Oracle and PostgreSQL databases and so, I am answering this question purely based on my own experience with them.

* Equivalent for Oracle’s ROWID
PostgreSQL contains its own system-defined columns and among such columns, you could use either ctid or oid as an equivalent for Oracle’s rowid.

ctid - It is a PostgreSQL system column of data type tid (tuple identifier). The column contains information about the physical blocks on a record level basis (row-level). However, this column value keeps changing whenever you update a record or perform full vacuum operations on a table. Therefore, you could use this column value as a unique row identifier only for temporary purposes, for example, deleting duplicates in a table. You cannot rely on this column value for deciding record level uniqueness on a table if you want to apply its usage for long-term use cases such as performing incremental inserts to a table based on the maximum/last inserted column value.

oid - Known as “object identifier”, oid contains unique values for a logical record/ row. It is of type oid (same as the column name). However, you need to explicitly create a table using “WITH OIDS” syntax for this column to be created for a table. You can check an example here [ http://www.sqlines.com/postgresql/oid ].

Note :

From PostgreSQL 12, oids cannot be used anymore. This is because oid is implemented using unsigned 4 byte integer and hence, it’s dangerous to rely on them for uniqueness especially when your tables are massively growing.

Based on my personal experience with PostgreSQL, it’s always better to use a user-defined column value such as Surrogate Key to uniquely identify records if your table does not have a primary key.

* Equivalent for Oracle’s ROWNUM
PostgreSQL does not have an exact equivalent for a rownum that you could use in your SQL “select” queries. However, you can mimic it by creating a unique value on the fly in your SQL queries.

For example (assuming your query over a table contains 3 columns),

[code]SELECT 
	COL_A,
	COL_B,
	COL_C,
	ROW_NUMBER() OVER (ORDER BY COL_A ASC) AS ROWNUM
	FROM _TABLE 
[/code]However, ROWNUM in Oracle is already assigned when you read a tuple from disk whereas, in the above query, you generate it after reading the tuples and hence, you need one more step when you actually want to apply the generated ROWNUM value.

Note :

You could also consider PostgreSQL’s limit as a close equivalent to ROWNUM, but you need to use one more functionality of PostgreSQL called offset when you want to mimic Oracle’s ROWNUM usage for a range filtering (such as ROWNUM between A and B). You can check for an example here [ http://www.sqlines.com/postgresql/limit_offset ].

Thanks for reading !!

நன்றி _/\_

ChatGPT · Answer

In PostgreSQL, the equivalents of Oracle's [code]ROWNUM[/code] and [code]ROWID[/code] concepts are achieved using different mechanisms:
ROWNUM Equivalent
Oracle's [code]ROWNUM[/code] is used to limit the number of rows returned by a query. In PostgreSQL, you can achieve similar functionality using the [code]LIMIT[/code] clause. For example:
[code]SELECT *
FROM your_table
LIMIT 10;[/code]
If you need to filter rows based on their order (like using [code]ROWNUM[/code] in an ordered query), you can use [code]ROW_NUMBER()[/code] with a Common Table Expression (CTE) or a subquery:
[code]WITH numbered_rows AS (
    SELECT *, ROW_NUMBER() OVER (ORDER BY some_column) AS rn
    FROM your_table
)
SELECT *
FROM numbered_rows
WHERE rn %3C= 10;[/code]
ROWID Equivalent
Oracle's [code]ROWID[/code] is a unique identifier for each row in a table, representing the physical location of the row. PostgreSQL does not have a direct equivalent, but you can use the [code]ctid[/code] system column, which serves a similar purpose by providing a unique identifier for rows within a table:
[code]SELECT ctid, *
FROM your_table;[/code]
Keep in mind that [code]ctid[/code] is specific to the physical storage of the row and can change after certain operations (like [code]VACUUM[/code] or [code]UPDATE[/code]).
Summary
 * ROWNUM is equivalent to [code]LIMIT[/code] or [code]ROW_NUMBER()[/code].
 * ROWID can be represented by [code]ctid[/code] in PostgreSQL. 
If you have any further questions about PostgreSQL or need examples, feel free to ask!

Ben Duncan · Answer

PostgreSQL ROW_NUMBER() Explained with Practical Examples [ https://www.postgresqltutorial.com/postgresql-row_number/ ]

Already been asked:

What is the PostgreSQL equivalent of Oracle's ROWNUM and ROWID? [ https://www.quora.com/What-is-the-PostgreSQL-equivalent-of-Oracles-ROWNUM-and-ROWID ]

Scott Emick · Answer

In MySQL you can use LIMIT to grab a subset of the query result. You must use order by to keep the order consistent.

LIMIT [OFFSET],[NumRows]

select * from customers LIMIT 1,10 returns 10 rows starting with the 2nd row.

MySQL 8 and later has the row() function to return the current row number.
before that, you must emulate it in sql. See the link below how to do that.

MySQL row_number, This Is How You Emulate It. [ https://www.mysqltutorial.org/mysql-row_number/ ]

Marcin Badtke · Answer

Oracle’s SYSDATE returns datetime of the database host with second precision and without time zone.

In PostgreSQL there is no such function. Closest is LOCALTIMESTAMP with microsecond precision. It returns datetime of the beginning of the transaction.

Robert Treat · Answer

Answering this question from a *developers* point of view, I think there are a few things that stand out as key differences.

1. Both have very advanced SQL capabilities, but you’ll need to learn the specifics for each database. Think “+” syntax for left joins or connect by in Oracle, vs ANSI standard syntax or WITH Recursive in Postgres. In general Postgres is more likely to use a standard way, and Oracle an “Oraclism”; better tends to be defined by what you are familiar with, but both have good capabilities.
2. Rownum is really powerful and often used by Oracle developers; in Postgres people tend to play tricks with generate_series() or limit / offset. Again, your preference is likely what you are used to working with.
3. Oracle has a robust language in pl/sql, and a much more robust package implementation that Postgres, however Postgres allows you to write language handlers in multiple languages, so you can use things like Python and R directly in the database. This is actually even more powerful than Oracle (imho), although it’s not as commonly used as Oracle packages.
4. Oracle has more advanced query tuning capabilities, and to be honest a more advanced query optimizer, although I find that what Postgres offers already goes far beyond what most developers will generally make use of, so this is probably a wash for 99% of developers out there.
5. Being Open Source, Postgres has a nod in breadth of libraries available for developers to connect into Postgres, however, in a few cases what Oracle offers is likely more polished than what you would get for Postgres. (Oracle + Java / JDBC comes to mind).
6. Postgres tends to feel much more lightweight for developers, so that they don’t mind installing and reinstalling development versions on their laptops. From what I have seen, developers tend to avoid installing Oracle as much as possible given it is a more cumbersome process, and the overhead is much higher.
7. That said, Postgres replication / failover is much less coordinated, which might affect how you need to write and manage your applications. Using something like Oracle RAC make this process somewhat easier (if not way more expensive).
Hopefully that helps. In the end, I find developers tend to be happier working with Postgres rather than Oracle, but my sample size is probably biased. I would say that there is a large set of younger developers who probably have never worked with Oracle but have with Postgres (think Rails or Django developers), so that may affect your ability to get help.

Adam Taylor · Answer

The Oracle TRUNC function is used to get the date with the time portion of the day truncated to a specific unit of measure. It operates according to the rules of the Gregorian calendar.

Its Syntax is:

[code]TRUNC(date [, fmt ])
[/code]PostgreSQL has a similar function called date_trunc(). It truncates a timestamp to specified precision, i.e.:

[code]date_trunc('datepart', field)
[/code]The datepart argument is the level of precision used to truncate the field, which can be one of the following:

* millennium
 * century
 * decade
 * year
 * quarter
 * month
 * week
 * day
 * hour
 * minute
 * second
 * milliseconds
 * microseconds
Here’s an example:

[code]date_trunc('hour', timestamp '2001-02-16 20:38:40')
[/code]The above returns ‘2001-02-16 20:00:00’.

The database client that I use is Navicat for PostgreSQL [ https://www.navicat.com/en/products/navicat-for-postgresql ]. I like that it can show me and even insert the correct syntax in my queries.

It also has auto completion, which is very helpful! Here is the date_truc() function:

I used it to look up this answer. ;-)

Best regards!

Adam

Greg Kemnitz · Answer

It’s a nonstandard SQL extension supported by a few DB engines, particularly Oracle. It is not part of the SQL standard, and isn’t supported on many engines.

Here’s a link to an Oracle page discussing it: ROWNUM Pseudocolumn [ https://docs.oracle.com/cd/B19306_01/server.102/b14200/pseudocolumns009.htm ]

In Oracle, the ROWNUM is the number of the fetched column from the query, ie if you fetch 10 rows with a query, the fifth row will be ROWNUM=5. (Oracle ROWNUMs start with 1)

You can duplicate this functionality in various ways in some other DB engines.

Aurelio Bautista · Answer

SQL cast operator can be used. Or the shorthand expression::int, expression::decimal … or … TO_NUMBER(string, format) function. I don't know if I ever knew it. I just put your question in Google search. I mean for TO_NUMBER, the cast with :: I use all the time because shorter than CAST(expression as numeric SQL type).

Earl Lewis · Answer

Straight from the docs.

ROWNUM

For each row returned by a query, the [code ]ROWNUM[/code] pseudocolumn returns a number indicating the order in which Oracle selects the row from a table or set of joined rows. The first row selected has a [code ]ROWNUM[/code] of 1, the second has 2, and so on.

You can use [code ]ROWNUM[/code] to limit the number of rows returned by a query, as in this example:

[code]SELECT * FROM employees WHERE ROWNUM %3C 10;
[/code]

Grant Fritchey · Answer

Wouldn’t the TO_NUMBER function [ https://www.postgresqltutorial.com/postgresql-to_number/#:~:text=The%20PostgreSQL%20TO_NUMBER%20%28%29%20function%20converts%20a%20character,arguments.%20String%20to%20be%20converted%20to%20a%20number. ] be about the same as the to_number function?

However, you can also use CAST and, a PostgreSQL short cut “::” [ https://learnsql.com/cookbook/how-to-convert-a-string-to-a-numeric-value-in-postgresql/ ] which functions as CAST.

Thanks for the answer request.

Andrew Droffner · Answer

Use the SQL Standard WITH RECURSIVE … statement [ https://www.postgresql.org/docs/12/queries-with.html ]. It is much more verbose than Oracle’s CONNECT BY… but most SQL RDBMS servers support WITH and Common Table Expressions CTE.

* PostgreSQL WITH [RECURSIVE] Queries (Common Table Expressions) [ https://www.postgresql.org/docs/12/queries-with.html ]

Art Kagel · Answer

ROWNUM is a pseudo-column in a query that returns/contains the ordinal number of a tuple within the data set. It was first supported by Oracle and since adopted by several other RDBMS systems for compatibility.

Gautam Gupta · Answer

ROWID is a Pseudocolumn in Oracle. Read about Pseudocolumn here [ https://www.quora.com/What-is-a-Pseudocolumn-in-SQL/answer/Gautam-Gupta-102 ].

ROWID Pseudocolumn in Oracle is of ROWID datatype. It is a string that represents the address of a row in the database.

Follow me at Gautam Gupta [ https://www.quora.com/profile/Gautam-Gupta-102 ] to learn more about Oracle and SQL.

That Banh · Answer

ROW_NUMBER is an analytic function. It assigns a unique number to each row to which it is applied (either each row in the partition or each row returned by the query), in the ordered sequence of rows specified in the order_by_clause , beginning with 1.

Manish K Singh · Answer

Yes, We can use it.

Example -

[code]SELECT * FROM MAIN_TABLE 
WHERE ROWNUM %3C 5 ORDER BY winame;
[/code]Regards | Manish K Singh [ https://www.quora.com/profile/Manish-K-Singh-10 ]

Larry Creager · Answer

ROWID is a built-in column that’s part of every query and represents the order in which rows were selected (not necessarily displayed.) MAX simply identifies the last such row selected.

Himanshu Raghav · Answer

Row number these function in SQL Server that allow us to assign rankings to the rows of the data the basically 4 types of Row number

1.Row number

2.Rank

3.Denise Rank

4.NTile

the syntax of Row number is Rank() Over ( {Partition_By_Clause} Order_By_Clause)

Steve Farmer · Answer

PostgreSQL and Oracle are both powerful, full-featured relational database systems, but have some key differences:

PostgreSQL is open source, Oracle is commercial - PostgreSQL is free to use/distribute, Oracle has licenses/fees
 PostgreSQL is available on all major platforms, Oracle is mainly used on Linux/UNIX
 PostgreSQL has a reputation for standards compliance and simplicity, Oracle is known for a variety of advanced features and high scalability/performance
 PostgreSQL has a very active open source community, Oracle's development is internal
 PostgreSQL licensing is very free and flexible, Oracle's licensing can be complex and costly for large deployments

So some reasons to prefer PostgreSQL would be:

Cost - Free and open source
 Simplicity - Easier to setup and maintain for basic uses
 Community - Active and helpful community if you need support
 Flexibility - Less restrictive licensing, and able to modify code if desired

Reasons to prefer Oracle would be:

Performance/Scalability - Very capable for large/enterprise deployments
 Advanced Features - Numerous advanced and enterprise-focused features
 Support - Direct support from Oracle available for paying customers

Overall it depends on your specific needs, budget, and other factors. Both are very capable databases, but have distinct strengths and weaknesses.

Boris Pinsky · Answer

Since MySql 8 you can do it with row_number() function