20.4.4.2 Select Tables

To issue a query that returns all records from an existing table, use the select() method without specifying search conditions. The following example selects all records from the city table in the world_x database.

mysql-py> db.city.select()
+------+------------+-------------+------------+-------------------------+
| ID   | Name       | CountryCode | District   | Info                    |
+------+------------+-------------+------------+-------------------------+
|    1 | Kabul      | AFG         | Kabol      |{"Population": 1780000}  |
|    2 | Qandahar   | AFG         | Qandahar   |{"Population": 237500}   |
|    3 | Herat      | AFG         | Herat      |{"Population": 186800}   |
...    ...          ...           ...          ...
| 4079 | Rafah      | PSE         | Rafah      |{"Population": 92020}    |
+------+------- ----+-------------+------------+-------------------------+
4082 rows in set (0.01 sec)

An empty set (no matching records) returns the following information:

Empty set (0.00 sec)

To issue a query that returns a set of table columns, use the select() method and specify the columns to return between square brackets. This query returns the Name and CountryCode columns from the city table.

mysql-py> db.city.select(["Name", "CountryCode"])
+-------------------+-------------+
| Name              | CountryCode |
+-------------------+-------------+
| Kabul             | AFG         |
| Qandahar          | AFG         |
| Herat             | AFG         |
| Mazar-e-Sharif    | AFG         |
| Amsterdam         | NLD         |
...                 ...
| Rafah             | PSE         |
| Olympia           | USA         |
| Little Falls      | USA         |
| Happy Valley      | USA         |
+-------------------+-------------+
4082 rows in set (0.00 sec)

To issue a query that returns rows matching specific search conditions, use the where() method to include those conditions. For example, the following example returns the names and country codes of the cities that start with the letter Z.

mysql-py> db.city.select(["Name", "CountryCode"]).where("Name like 'Z%'")
+-------------------+-------------+
| Name              | CountryCode |
+-------------------+-------------+
| Zaanstad          | NLD         |
| Zoetermeer        | NLD         |
| Zwolle            | NLD         |
| Zenica            | BIH         |
| Zagazig           | EGY         |
| Zaragoza          | ESP         |
| Zamboanga         | PHL         |
| Zahedan           | IRN         |
| Zanjan            | IRN         |
| Zabol             | IRN         |
| Zama              | JPN         |
| Zhezqazghan       | KAZ         |
| Zhengzhou         | CHN         |
...                 ...
| Zeleznogorsk      | RUS         |
+-------------------+-------------+
59 rows in set (0.00 sec)

You can separate a value from the search condition by using the bind() method. For example, instead of using "Name = 'Z%' " as the condition, substitute a named placeholder consisting of a colon followed by a name that begins with a letter, such as name. Then include the placeholder and value in the bind() method as follows:

mysql-py> db.city.select(["Name", "CountryCode"]).\
              where("Name like :name").bind("name", "Z%")

To issue a query using the AND operator, add the operator between search conditions in the where() method.

mysql-py> db.city.select(["Name", "CountryCode"]).\
               where("Name like 'Z%' and CountryCode = 'CHN'")
+----------------+-------------+
| Name           | CountryCode |
+----------------+-------------+
| Zhengzhou      | CHN         |
| Zibo           | CHN         |
| Zhangjiakou    | CHN         |
| Zhuzhou        | CHN         |
| Zhangjiang     | CHN         |
| Zigong         | CHN         |
| Zaozhuang      | CHN         |
...              ...
| Zhangjiagang   | CHN         |
+----------------+-------------+
22 rows in set (0.01 sec)

To specify multiple conditional operators, you can enclose the search conditions in parenthesis to change the operator precedence. The following example demonstrates the placement of AND and OR operators.

mysql-py> db.city.select(["Name", "CountryCode"]).\
where("Name like 'Z%' and (CountryCode = 'CHN' or CountryCode = 'RUS')")
+-------------------+-------------+
| Name              | CountryCode |
+-------------------+-------------+
| Zhengzhou         | CHN         |
| Zibo              | CHN         |
| Zhangjiakou       | CHN         |
| Zhuzhou           | CHN         |
...                 ...
| Zeleznogorsk      | RUS         |
+-------------------+-------------+
29 rows in set (0.01 sec)

You can apply the limit(), order_by(), and offset() methods to manage the number and order of records returned by the select() method.

To specify the number of records included in a result set, append the limit() method with a value to the select() method. For example, the following query returns the first five records in the country table.

mysql-py> db.country.select(["Code", "Name"]).limit(5)
+------+-------------+
| Code | Name        |
+------+-------------+
| ABW  | Aruba       |
| AFG  | Afghanistan |
| AGO  | Angola      |
| AIA  | Anguilla    |
| ALB  | Albania     |
+------+-------------+
5 rows in set (0.00 sec)

To specify an order for the results, append the order_by() method to the select() method. Pass to the order_by() method a list of one or more columns to sort by and, optionally, the descending (desc) or ascending (asc) attribute as appropriate. Ascending order is the default order type.

For example, the following query sorts all records by the Name column and then returns the first three records in descending order .

mysql-py> db.country.select(["Code", "Name"]).order_by(["Name desc"]).limit(3)
+------+------------+
| Code | Name       |
+------+------------+
| ZWE  | Zimbabwe   |
| ZMB  | Zambia     |
| YUG  | Yugoslavia |
+------+------------+
3 rows in set (0.00 sec)

By default, the limit() method starts from the first record in the table. You can use the offset() method to change the starting record. For example, to ignore the first record and return the next three records matching the condition, pass to the offset() method a value of 1.

mysql-py> db.country.select(["Code", "Name"]).order_by(["Name desc"]).limit(3).offset(1)
+------+------------+
| Code | Name       |
+------+------------+
| ZMB  | Zambia     |
| YUG  | Yugoslavia |
| YEM  | Yemen      |
+------+------------+
3 rows in set (0.00 sec)