SELECT id,name,info FROM table LIMIT 5
the result Set should be contains 5 rows wich is The first 5 rows of the table,but is any exception about this usage? .the table like this :
SELECT * FROM table limit 10;
1. company_id company_name tel
1 TCL集团股份有限公司 0752-2288333
2 UNITEDSTACK（北京）科技有限公司 15727325616
3 《市政技术》杂志社有限公司 13401070358
4 《网络安全技术与应用》杂志社有限公司 010-62765013
5 《艺术市场》杂志社股份有限公司 64271947
7 一呼医知己健康咨询（北京）有限公司 010-62957992
8 一呼（北京）电子商务有限公司 62957992
9 一汽轿车股份有限公司 0431-85782608
10 一通万通商务服务（北京）有限公司 010-68061805
I use the first sql the result is normal:like this
SELECT company_id,company_name,tel FROM table LIMIT 5;
1. 1 TCL集团股份有限公司 0752-2288333
2 UNITEDSTACK（北京）科技有限公司 15727325616
3 《市政技术》杂志社有限公司 13401070358
4 《网络安全技术与应用》杂志社有限公司 010-62765013
5 《艺术市场》杂志社股份有限公司 64271947
However I use the second sql like this :
SELECT comapny_id,company_name FROM table LIMIT 5;
1275992
1758051
2990914
5241776
5344925
We are seeing the result is not the 5 rows of the table obviously,the difference of these fileds is that company_id is a primary key,company_name is a type of MUL.can you help me?thank you very much!
the result Set should be contains 5 rows wich is The first 5 rows of
the table,but is any exception about this usage?
Only the first part of this statement is correct. Your query returns 5 rows from the query. However, those are 5 indeterminate rows.
SQL tables represent unordered sets. Hence, there is no first five rows in a table. If you want your result set ordered, then you need to include an order by clause. Often, an auto-incremented id is used for this purpose, because such an id captures the order that rows are inserted into the table.
Related
select * from "Test"."EMP"
id
1
2
3
4
5
Select SUM(1) FROM "Test"."EMP";
Select SUM(2) FROM "Test"."EMP";
Select SUM(3) FROM "Test"."EMP";
why the output of these queries is?
5
10
15
And
I don't understand why they write table name like this "Test"."EMP"
your table has 5 records. the statement select 1 from test.emp returns 5 records with values as 1 for all 5 records.
id
1
1
1
1
1
This is because db engine simply returns 1 for each existing record without reading the contents of the cell. and same happens for select <any static value> from test.emp
same happens for 2 and 3
id
2
2
2
2
2
hence there are 5 records returned with the static values and sum of those values will be the product of static number passed in the select statement and total records in the table
additional fact: It is always recommended to perform count(1) than count(*) as it consumes less resource and hence less load on the server
I don't think it's "Test"."EMP" with double quotes.. it's probably `Test`.`EMP` with backticks instead. The definition means its database_name.table_name. This is the recommended format to get the correct table_name from database_name; in this case, you're specifically making the syntax to query from `Test`.`EMP`. Read more about identifier qualifiers.
As for SUM(x), the x get's repeated according to the rows present in the table. So SUM(1) on 5 rows is 1+1+1+1+1, SUM(2) on 5 rows is 2+2+2+2+2, and so on.
We have following table with columns:
CategoryId | CategoryName with CategoryId as primary-key.
We have following data:
0 Other
1 Bumper
2 Door
3 Roof
4 Fender
I use select * from these table and i get rows in the above sequence only i.e. 0 first and 4 at last.
Is there any way I can get 0 at last? i.e. 1,2,3,4,0?
select * from yourtable order by CategoryId=0,CategoryId
You can use arbitrary expressions in an order by clause. By first ordering by CategoryId=0, you get all records for which that is false, followed by records (obviously only one, since it is the primary key) for which it is true. Then each of those sets of records are sorted by CategoryId.
i have table lets say - Students,
with 5 records and id(s) are 1 to 5, now i want to select the records - in a way that result should come like given sorting order of id column
id column should be resulted - 5,2,1,3,4
is there any other way to do this - then separate db calls for ids?
single db call ?
I guess if you really want a hard-coded order, you could do something like this:
order by case id
when 5 then 0
when 2 then 1
when 1 then 2
when 3 then 3
when 4 then 4
else 999
end
Or more simply (as #Strawberry points out in the comments):
order BY FIELD(id,4,3,1,2,5) desc
I have 1 MYSQL table with 8000 records. I would like to query First name, Middle name, and Last name by the first characters of their full name. For instance, i have 40 rows of records (First name, Middle name, and Last name) which their first character of their name is SSS. My question is, how do i query "SSS" to only return 6 results and when i query "SSS" again i need another 6 results and so on until all the 40 records query ends.
I used the following query but only return the first 6 results and when i query "SSS" the next time, it returns the same results over and over. Please i need your help.
SELECT *
FROM Table
WHERE (UPPER(FName) LIKE UPPER('S%')
AND UPPER(MName) LIKE UPPER('S%')
AND UPPER(LName) LIKE UPPER('S%')
ORDER BY ID
LIMIT 6 OFFSET 0
Thanks in advance.
You're ordering by ID - good. Remember max ID of the last returned data set and when you query next time add condition ID > your_last_max_id
Second time, change offset:
LIMIT 6 OFFSET 6
and then
LIMIT 6 OFFSET 12
etc.
i have a table with about 100 rows , and i want every time to get rows between number and number , like this
if `i=1` i want to get the rows `0 1 2 3 4`
if `i=2` i want to get the rows `5 6 7 8 9`
if `i=3` i want to get the rows `10 11 12 13 14`
and maybe the last value of i will just take 3 or 4 rows not 5
i think the solution will be something like this
select * from question limit (i-1)*5 , i*5-1
but doesn't work , cos i don't know how to use variable in a query , and when i tried it for i=1 it doesn't work and i got a syntax error
The first parameter to LIMIT is the zero-based starting row index. The second one is the number of rows. So, if you're always looking for five rows:
SELECT * FROM question LIMIT (i-1)*5 , 5
(You'll have to calculate (i-1)*5 with whatever language you're using to build the query, and pass an actual number to MySQL).