SQL, Python & More for DuckDB - Page 3

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Add a unique column (key) to an existing table in DuckDBSQL

We can use DuckDB's `SEQUENCE` to add a unique key to a table.Many source data files (such as CSV files) do not include a unique key.

Execute this SQL

CREATE TABLE tbl (s VARCHAR);

INSERT INTO tbl VALUES ( 'hello'),('world');

CREATE SEQUENCE id_sequence;

ALTER TABLE tbl ADD COLUMN id INTEGER DEFAULT nextval ('id_sequence');

SELECT * FROM tbl;
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colorcrow

Created 08/31/24

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Query from Google SheetsSQL

Sometimes you have data over in Google Sheets and you want quickly and easily load it into DuckDB. With read_csv and the Google Sheets 'export to csv', its just one line of code.

Execute this SQL

-- you will need to create a sharelink for your sheet.
-- note the tab id (gid) and sheet id (in the url)

from read_csv('https://docs.google.com/spreadsheets/d/{sheet_id}/export?format=csv&gid={tab_id}')
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Jacob Matson

Created 08/28/24

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Emulate the Initcap functionSQL

In many database systems, there is a SQL function called something like INITCAP which capitalizes the first letter of all the words in a text string. Unfortunately, DuckDB doesn’t have this built-in, so let’s see if we can emulate it using function chaining and list comprehension.

Execute this SQL

SELECT ([upper (x[1])||x[2:] 
for x in 
(
'the quick brown fox jumped over the lazy dog'
).string_split(' ')]).list_aggr('string_agg',' ') 
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Thomas Reid

Created 08/21/24

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Updating CSV files in-placeSQL

DuckDB allows updating CSV files in-place.

Execute this SQL

COPY (FROM VALUES ('foo', 10/9), ('bar', 50/7), ('qux', 9/4) t(s, x))
TO 'example.csv';

COPY (SELECT s FROM 'example.csv') TO 'example.csv';
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Gábor Szárnyas

Created 08/13/24

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Specifying types in the CSV loaderSQL

We can specify types for the `read_csv` function on a per-column basis.

Execute this SQL

COPY (FROM VALUES ('foo', 10/9), ('bar', 50/7), ('qux', 9/4) t(s, x))
TO 'example.csv';

CREATE OR REPLACE TABLE example AS
    FROM read_csv('example.csv', types = {'x': 'DECIMAL(15, 3)'});
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Gábor Szárnyas

Created 08/13/24

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Deterministically shuffling dataSQL

Sometimes it's beneficial to shuffle data sets in a deterministic, repeatable way. We can achieve this by using the `hash` function on the `rowid` pseudocolumn.

Execute this SQL

COPY (FROM VALUES ('foo', 10/9), ('bar', 50/7), ('qux', 9/4) t(s, x))
TO 'example.csv';

CREATE OR REPLACE TABLE example AS FROM 'example.csv';
FROM example ORDER BY hash(rowid + 42);
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Gábor Szárnyas

Created 08/13/24

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Copying the schema of a tableSQL

We can use `LIMIT` to copy the schema of an existing table without repeating the specification of its column names/types.

Execute this SQL

COPY (FROM VALUES ('foo', 10/9), ('bar', 50/7), ('qux', 9/4) t(s, x))
TO 'example.csv';

CREATE TABLE tbl AS
    FROM example
    LIMIT 0;
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Gábor Szárnyas

Created 08/13/24

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Pretty-printing floating-pont numbersSQL

By casting the result to a `DECIMAL` with a fixed number of digits after the decimal point, we can pretty-print it while keeping it as a numeric value.

Execute this SQL

COPY (FROM VALUES ('foo', 10/9), ('bar', 50/7), ('qux', 9/4) t(s, x))
TO 'example.csv';

SELECT x::DECIMAL(15, 3) AS x
FROM 'example.csv';
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Gábor Szárnyas

Created 08/13/24