Tha an SELECT
tha aithris ann an SQL air a chleachdadh gus dàta fhaighinn air ais bho chlàr stòr-dàta.
Faodaidh sinn an SELECT
a chleachdadh aithris gus dàta fhaighinn bhon cholbh / na colbhan ainmichte no na colbhan uile.
Tha an SELECT
tha an co-chòrdalachd a leanas aig an aithris:
SELECT column1, column2, ... FROM table_name;
Osbarr tha clàr againn air a bheil “Luchd-obrach” leis an dàta a leanas:
+------------+-----------+----------+------------+ | EmployeeID | FirstName | LastName | Department | +------------+-----------+----------+------------+ | 1
| Mark
| Otto
| Finance | | 2
| Jacob
| Thornton | IT
| | 3
| Su
| Bird
| Marketing | | 4
| Sam
| Burger | IT
| +------------+-----------+----------+------------+
Gus colbh “Roinn” a thaghadh bhon chlàr “Luchd-obrach”:
SELECT Department FROM Employees;
Toradh:
+------------+ | Department | +------------+ | Finance | | IT
| | Marketing | | IT
| +------------+
Gus colbhan “Roinn” agus “EmployeeID” a thaghadh bhon chlàr “Luchd-obrach”:
SELECT EmployeeID, Department FROM Employees;
Toradh:
+------------+------------+ | EmployeeID | Department | +------------+------------+ | 1
| Finance | | 2
| IT
| | 3
| Marketing | | 4
| IT
| +------------+------------+
Gus na colbhan uile a thaghadh bhon chlàr “Luchd-obrach”:
SELECT * FROM Employees;
Toradh:
+------------+-----------+----------+------------+ | EmployeeID | FirstName | LastName | Department | +------------+-----------+----------+------------+ | 1
| Mark
| Otto
| Finance | | 2
| Jacob
| Thornton | IT
| | 3
| Su
| Bird
| Marketing | | 4
| Sam
| Burger | IT
| +------------+-----------+----------+------------+
Faodaidh sinn na toraidhean bho a SELECT
a shìoladh ceist le bhith a ’cleachdadh an WHERE
clàs.
Mar eisimpleir, airson gach neach-obrach san “Roinn TF” a thaghadh cleachd:
SELECT * FROM Employees WHERE Department='IT'
Toradh:
+------------+-----------+----------+------------+ | EmployeeID | FirstName | LastName | Department | +------------+-----------+----------+------------+ | 2
| Jacob
| Thornton | IT
| | 4
| Sam
| Burger | IT
| +------------+-----------+----------+------------+
Mar an ceudna, airson gach Ids neach-obrach a thaghadh a tha san “Roinn TF” a bhios sinn a ’cleachdadh:
SELECT EmployeeID FROM Employees WHERE Department='IT'
Toradh:
+------------+ | EmployeeID | +------------+ | 2
| | 4
| +------------+