Reading and writing data

PrerequisitesPrerequisites

To run queries, you will need to create a database and a table in it.

SQL queries in the management consoleSQL queries in the management console

To send an SQL query to a database from the management console:

1. In the management console, select the folder with the desired DB.
2. In the list of services, select Managed Service for YDB.
3. Select the database from the list.
4. Go to the Navigation tab.
5. Click New SQL query and enter the query text. When making queries, you can use the following templates:
   • To use one of the standard templates, select it from the drop-down list to the right of the New SQL query button.
   • To populate a template with data from a specific table, click in the row next to the table and select a template.
6. Click Run.

Insert and update dataInsert and update data

To insert data into YDB, use the REPLACE, UPSERT, and INSERT statements.

When executing REPLACE and UPSERT statements, a blind write is performed. With an INSERT statement, data is read before writing. This ensures that the primary key is unique.

We recommend using REPLACE and UPSERT statements to write and modify data.

A single REPLACE, UPSERT, or INSERT query can insert multiple rows into a table.

REPLACE INTO episodes (series_id, season_id, episode_id, title) VALUES (1, 1, 1, "Yesterday's Jam");
REPLACE INTO episodes (series_id, season_id, episode_id, title) VALUES (1, 1, 2, "Calamity Jen");

REPLACEREPLACE

Once you create the series, seasons, and episodes tables, you can insert data into the table using the REPLACE statement. Basic syntax:

REPLACE INTO <table_name> (<column_list>) VALUES (<list_of_added_values>);

The REPLACE statement is used to add a new or change an existing row at a given value of the primary key. If a row with the specified primary key value does not exist, it is created. If the row exists already, the column values of the existing row are replaced with the new values. The values of columns not involved in the operation are set to their default values. This is the only way the UPSERT statement is different.

Data added using the following code sample will be used later in this section.

REPLACE INTO series (series_id, title, release_date, series_info)
VALUES
  (
    1,
    "IT Crowd",
    CAST(Date("2006-02-03") AS Uint64),
    "The IT Crowd is a British sitcom produced by Channel 4, written by Graham Linehan, produced by Ash Atalla and starring Chris O'Dowd, Richard Ayoade, Katherine Parkinson, and Matt Berry."
  ),
  (
    2,
    "Silicon Valley",
    CAST(Date("2014-04-06") AS Uint64),
    "Silicon Valley is an American comedy television series created by Mike Judge, John Altschuler and Dave Krinsky. The series focuses on five young men who founded a startup company in Silicon Valley."
  )
;

REPLACE INTO seasons (series_id, season_id, title, first_aired, last_aired)
VALUES
  (1, 1, "Season 1", CAST(Date("2006-02-03") AS Uint64), CAST(Date("2006-03-03") AS Uint64)),
  (1, 2, "Season 2", CAST(Date("2007-08-24") AS Uint64), CAST(Date("2007-09-28") AS Uint64)),
  (2, 1, "Season 1", CAST(Date("2014-04-06") AS Uint64), CAST(Date("2014-06-01") AS Uint64)),
  (2, 2, "Season 2", CAST(Date("2015-04-12") AS Uint64), CAST(Date("2015-06-14") AS Uint64))
;

REPLACE INTO episodes (series_id, season_id, episode_id, title, air_date)
VALUES
  (1, 1, 1, "Yesterday's Jam", CAST(Date("2006-02-03") AS Uint64)),
  (1, 1, 2, "Calamity Jen", CAST(Date("2006-02-03") AS Uint64)),
  (2, 1, 1, "Minimum Viable Product", CAST(Date("2014-04-06") AS Uint64)),
  (2, 1, 2, "The Cap Table", CAST(Date("2014-04-13") AS Uint64))
;

UPSERTUPSERT

The UPSERT statement is used to add a new or change an existing row at a given value of the primary key. If a row with the specified primary key value does not exist, it is created. If the row exists already, the column values of the existing row are replaced with the new values. However, the values of columns not involved in the operation are not changed. This is what makes it different from the REPLACE statement.

The code below inserts one row of data into the episodes table.

UPSERT INTO episodes
(
  series_id,
  season_id,
  episode_id,
  title,
  air_date
)
VALUES
(
  2,
  1,
  3,
  "Test Episode",
  CAST(Date("2018-08-27") AS Uint64)
)
;

INSERTINSERT

The INSERT statement is used to insert one or more rows. If you try to insert a row into a table with an existing primary key value, YDB returns the following error message: Transaction rolled back due to constraint violation: insert_pk..

The code below inserts one row of data into the episodes table.

INSERT INTO episodes
(
  series_id,
  season_id,
  episode_id,
  title,
  air_date
)
VALUES
(
  2,
  5,
  21,
  "Test 21",
  CAST(Date("2018-08-27") AS Uint64)
)
;

UPDATEUPDATE

The UPDATE statement changes the values of columns for the table rows filtered by the WHERE clause. Basic syntax:

UPDATE <table_name> SET <column_1_name>=<new_column_1_value>, ... ,<column_N_name>=<new_column_N_value> WHERE <condition_for_row_filter>;

UPDATE statements cannot change primary key values. Enter and execute the following UPDATE statement to change the value of the title column from "Test Episode" to "Test Episode Updated" for the episode with series_id = 2, season_id = 1, and episode_id = 3.

UPDATE episodes
SET title="Test Episode Updated"
WHERE
  series_id = 2
  AND season_id = 1
  AND episode_id = 3
;

DELETEDELETE

The DELETE statement deletes the rows from the table filtered by the WHERE clause. The code below removes an episode with series_id = 2, season_id = 5, and episode_id = 21 from the episodes table.

DELETE
FROM episodes
WHERE
  series_id = 2
  AND season_id = 5
  AND episode_id = 21
;

Query data using SELECTQuery data using SELECT

To read data in the table, use the SELECT statement.

To query data from the series table, execute the code shown below.

SELECT
  series_id,
  title AS series_title,
  CAST (release_date AS Date) AS release_date
FROM series;

You can use an asterisk to select all the columns in a table. To obtain the values of all columns from the series table, execute the code shown below.

SELECT
  *
FROM series;

Make a parameterized queryMake a parameterized query

Use parameterized queries to improve performance by reducing the frequency of compiling and recompiling your queries.

Example

DECLARE $seriesId AS Uint64;
DECLARE $seasonId AS Uint64;

$seriesId = 1;
$seasonId = 2;

SELECT sa.title AS season_title, sr.title AS series_title
FROM seasons AS sa
INNER JOIN series AS sr
ON sa.series_id = sr.series_id
WHERE sa.series_id = $seriesId AND sa.season_id = $seasonId;