Python · Theory

SELECT

Theory

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SELECT

SELECT is about talking to a database from Python. Pattern is always: connect → cursor → execute → fetch or commit → close.

For SELECT: use ? placeholders (or the driver’s params). Never build SQL with + user text — that is injection. sqlite3 is in the stdlib for practice; MySQL/Mongo need a driver.

SELECT on the board — insert Asha, select her back, print the name. Same idea on MySQL. Close the connection.

SELECT — output — [('Asha',)]. fetchall reads rows.

Exam tip

Steps in order: connect → execute → fetch/commit → close. Mention placeholders.

Example

# SELECT
import sqlite3
con = sqlite3.connect(":memory:")
cur = con.cursor()
cur.execute("create table t(name text)")
cur.execute("insert into t values('Asha')")
print(cur.execute("select name from t").fetchall())
con.close()

SELECT — output: [('Asha',)]. fetchall reads rows.

Short notes

DefSELECT uses connect + cursor + SQL/API.
RuleSELECT — parameterized queries. Never + user text into SQL.
RememberSELECT — commit after write. close when done.
TrapSELECT — open connections left hanging; passwords in source.

# SELECT import sqlite3 con = sqlite3.connect(":memory:") cur = con.cursor() cur.execute("create table t(name text)") cur.execute("insert into t values('Asha')") print(cur.execute("select name from t").fetchall()) con.close()

SELECT

Example

Short notes

Questions

SELECT

Example

Short notes

Questions