This MySQL Select lesson is for a beginner. Read the short notes, run each example, then change one name or number and run it again.
SELECT reads columns from a table. SELECT * reads every column. Naming the columns keeps the result stable if the table gains a column later.
The example lists one column from the in-memory rows.
Example 1: Start here
SELECT name FROM learner is the statement this loop imitates.
rows = [{"name": "Meera", "city": "Chennai"}, {"name": "Arun", "city": "Madurai"}] # a list; the values stay in this order
print([row["name"] for row in rows]) # in is True when the value is found
Example 2: Filter the rows
MySQL Select is easier to see as a list of records. The filter keeps every row whose seats value is at least 10.
rows = [{"topic": "MySQL Select", "seats": 37}, {"topic": "SQL", "seats": 12}] # a list; the values stay in this order
print([row["topic"] for row in rows if row["seats"] >= 10]) # keep the items that pass the test
Example 3: Update one field
An update changes one field and leaves the rest of the record alone. On a database you would run an UPDATE or an update_one for the same change.
row = {"topic": "MySQL Select", "seats": 37} # a dictionary; each key has one value
row["seats"] = row["seats"] + 1 # change this one field
print(row)
Example 4: Count the matches
Counting matches is the idea behind COUNT(*). Here the number 37 appears twice.
rows = [37, 4, 37] # a list; the values stay in this order
print(sum(1 for value in rows if value == 37)) # keep the items that pass the test
SELECT name FROM learner is the statement this loop imitates.
