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 DB you need.
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 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 the series, seasons, and episodes tables are created, you can insert data into a table using the REPLACE statement. Basic syntax:

REPLACE INTO <table_name> (<list_of_columns>) VALUES (<list_of_values_to_add>);

Use REPLACE statements to add a new row or change an existing row based on the specified value of the primary key. If a row with the specified primary key value does not exist, it will be created. If the row already exists, the column values of the existing row will be replaced with the new values. The values of columns not involved in the operation are set to their default values. This is the only difference from the UPSERT statement.

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

Use UPSERT statement to add a new row or change an existing one based on a specified value of the primary key. If a row with the specified primary key value does not exist, it will be created. If the row already exists, the column values of the existing row will be replaced with the new values. However, the values of the columns not involved in the operation will not be changed. This is the only difference 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

Use INSERT statements to insert one or more rows. If you try to insert a row into a table with an existing primary key value, YDB will return 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 column values for table row filtered by the WHERE predicate. Basic syntax:

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

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 table rows filtered by a WHERE predicate. The code below removes the 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

Use the SELECT statement to read data from a table.

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, run 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;