Aithris Tagh SQL

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.



SQL SELECT Syntax

Tha an SELECT tha an co-chòrdalachd a leanas aig an aithris:


SELECT column1, column2, ... FROM table_name;

Eisimpleirean aithris SQL SELECT

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
| +------------+-----------+----------+------------+


SELECT Bho cholbh

Gus colbh “Roinn” a thaghadh bhon chlàr “Luchd-obrach”:


SELECT Department FROM Employees;

Toradh:

+------------+ | Department | +------------+ | Finance | | IT
| | Marketing | | IT
| +------------+


SELECT Bho ioma-cholbhan

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
| +------------+------------+


SELECT * Aithris

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
| +------------+-----------+----------+------------+


Filter Toraidhean a ’cleachdadh clàs

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

| +------------+