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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Updating CSV files in-placeSQL
DuckDB allows updating CSV files in-place.
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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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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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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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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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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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UK Bank HolidaysSQL
The UK government publish the UK bank holidays as a JSON object at a public endpoint. DuckDB can read the data from the endpoint, unpivot it, and expand it in a few lines!
Execute this SQL
/* division, title, date, notes, bunting */ select division, unnest(events.events, recursive:=true) from ( unpivot 'https://www.gov.uk/bank-holidays.json' on "england-and-wales", "scotland", "northern-ireland" into name division value events )
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Parquet to ExcelSQL
Editor's note: although not very intuitive, format for MS Excel XLSX files is provided by the spatial extension. While other snippets show you how to read Excel files, this shows you how to write data from a named Parquet file (or any DuckDB resultset) to Excel.
Execute this SQL
INSTALL spatial; LOAD spatial; COPY (SELECT * FROM 'source.parquet') TO 'target.XLSX' WITH (FORMAT GDAL, DRIVER 'XLSX');
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