How to select only 1 row from oracle sql?

问题

I want to use oracle syntax to select only 1 row from table DUAL. For example, I want to execute this query:

SELECT user 
  FROM DUAL

...and it'd have, like, 40 records. But I need only one record. ...AND, I want to make it happen without a WHERE clause.

I need something in the table_name field such as:

SELECT FirstRow(user) 
  FROM DUAL

回答1:

You use ROWNUM.

ie.

SELECT user FROM Dual WHERE ROWNUM = 1

http://docs.oracle.com/cd/B19306_01/server.102/b14200/pseudocolumns009.htm

回答2:

I found this "solution" hidden in one of the comments. Since I was looking it up for a while, I'd like to highlight it a bit (can't yet comment or do such stuff...), so this is what I used:

SELECT * FROM (SELECT [Column] FROM [Table] ORDER BY [Date] DESC) WHERE ROWNUM = 1

This will print me the desired [Column] entry from the newest entry in the table, assuming that [Date] is always inserted via SYSDATE.

回答3:

This syntax is available in Oracle 12c:

select * from some_table fetch first 1 row only;
select * from some_table fetch first 1 rows only;
select * from some_table fetch first 10 row only;
select * from some_table fetch first 10 rows only;

^^I just wanted to demonstrate that either row or rows (plural) can be used regardless of the plurality of the desired number of rows.)

回答4:

As far as I know, the dual table in Oracle is a special table with just one row. So, this would suffice:

SELECT user
FROM dual

回答5:

👌 The answer is:

You should use nested query as:

SELECT *
FROM ANY_TABLE_X 
WHERE ANY_COLUMN_X = (SELECT MAX(ANY_COLUMN_X) FROM ANY_TABLE_X) 

=> In PL/SQL "ROWNUM = 1" is NOT equal to "TOP 1" of TSQL.

So you can't use a query like this: "select * from any_table_x where rownum=1 order by any_column_x;" Because oracle gets first row then applies order by clause.

回答6:

There is no limit 1 condition (thats MySQL / PostgresSQL) in Oracle, you need to specify where rownum = 1.

回答7:

"FirstRow" Is a restriction and therefor it's place in the where clause not in the select clause. And it's called rownum

select * from dual where rownum = 1;

回答8:

we have 3 choices to get the first row in Oracle DB table.

1) select * from table_name where rownum= 1 is the best way

2) select * from table_name where id = ( select min(id) from table_name)

3)

select * from 
    (select * from table_name order by id)
where rownum = 1

回答9:

If any row would do, try:

select max(user)  
from table;

No where clause.

回答10:

select name, price
  from (
    select name, price, 
    row_number() over (order by price) r
      from items
  )
where r between 1 and 5; 

回答11:

select a.user from (select user from users order by user) a where rownum = 1

will perform the best, another option is:

select a.user 
from ( 
select user, 
row_number() over (order by user) user_rank, 
row_number() over (partition by dept order by user) user_dept_rank 
from users 
) a 
where a.user_rank = 1 or user_dept_rank = 2

in scenarios where you want different subsets, but I guess you could also use RANK() But, I also like row_number() over(...) since no grouping is required.

回答12:

More flexible than select max() is:

select distinct first_row(column_x) over (order by column_y,column_z,...) from Table_A

来源：https://stackoverflow.com/questions/8919481/how-to-select-only-1-row-from-oracle-sql