Using hsql

hsql is your agent’s favorite SQL client. It the headless CLI for Harlequin, and shares the same config and query engine, with an interface optimized for agents, scripts, and automations.

hsql is packaged with Harlequin, so you install it by installing Harlequin.

hsql can connect to dozens of databases using the same adapter plug-ins as Harlequin.

Running hsql

Once hsql is installed, you run it from the command line. If you have used psql or the duckdb CLI, hsql will feel familiar, but hsql has the major advantage that is works with most databases and provides the same interface and produces the same output, regardless of the connected database. This means you (and your agent) can learn one tool, instead of several. In your shell, all hsql commands take the same form:

$ hsql [OPTIONS] [CONN_STR]

where [OPTIONS] is 0 or more pairs of the form --[option-name] [option-value], and [CONN_STR] is 0 or more connection strings. [OPTIONS] are composed of both hsql options and adapter options. For a full list of options, run hsql with the --help option:

$ hsql --help

Database Adapters

lightbulb icon Tip
hsql and Harlequin use the same options for defining adapters, connection strings, and adapter options. If you can connect to your database with Harlequin, just replace harlequin with hsql.

If you are new to Harlequin, see Running Harlequin for more information.

Like Harlequin, hsql defaults to using its DuckDB database adapter, which ships with hsql and includes the full DuckDB in-process database.

Run a query against an in-memory DuckDB session, run hsql and pass in a query with the -c option:

$ hsql -c "select 1"
 1
---
 1
(1 row)

To connect to a local DuckDB or SQLite database file, pass the path as a connection string; note that the --adapter option has a short alias, -a:

$ hsql -a sqlite "path/to/sqlite.db" -c "select * from users"
 id | name
----+---------
 1  | Ted
 2  | Patrick
(2 rows)

Other adapters take URIs or DSNs as connection strings; for example, Postgres:

$ hsql -a postgres "postgresql://example.com/postgres:5432" -c "select * from invoices"
lightbulb icon Tip
You should use [profiles](../config-file/index) to keep credentials out of your shell history.

Configuring hsql and Using Profiles

hsql supports a number of options for setting the query limit, configuring output formats, and defining connection parameters. Options can be passed as command-line flags, or read from config files. Config files store configurations under separate profiles, so you can easily switch between databases by reading from different profiles with the -P option:

$ hsql -P prod -c "select count(*) from orders" --csv
hsql -P dev -c "select * from users" --vertical --limit 5
hsql -P warehouse -c "..." --parquet -o invoices.pq

Data Layouts and File Formats

hsql supports all of the following formats for displaying and writing data:

  • table
  • markdown (alias: md)
  • vertical
  • csv
  • tsv
  • json
  • jsonl (alias: ndjson)
  • parquet
  • orc
  • feather (alias: arrow)
  • none (suppresses output)

You can select a format with the --format <name> or using the shorthand --<name>, so these are equivalent: --format csv, --csv.

Some layouts can present the results from multiple queries. Others will raise an error and exit with code 2 if multiple queries are executed.

Additionally, for any layout, pass --stats to print summary info as JSON to stderr:

$ hsql -c "select 1" --format none  --stats
&lbrace"status":"ok","statements":1,"rows":1,"truncated":false,"limit":500,"elapsed_ms":1,"columns":[&lbrace"name":"1","type":"#"&rbrace]&rbrace

Scripting with hsql

lightbulb icon Warning
To make hsql safe and efficient for agents, by default hsql applies a 500-row limit to all queries. To remove this limit, use --limit -1 or set limit = -1 in your profile. If limits truncate data, hsql will print a warning on stderr; we recommend that you do NOT suppress or redirect that message so do NOT use hsql with 2>/dev/null.

hsql can write data to files, either with the -o option or by piping output (hsql only writes data to stdout; other messages go to stderr):

$ hsql -P prod --limit -1 -c "select * from users" --parquet -o "users.pq"
hsql -P prod --limit -1 -c "select * from users" --csv > users.csv

hsql can execute multiple statements in one invocation, and supports several methods for doing so:

  • Pass -c multiple times
  • Include multiple queries, separated by ;, in one -c option
  • Pass one or more .sql files with -f, with multiple statements in each
  • Use --results to define which queries output data to stdout
  • Use --on-error to either stop or continue if one or more queries produces an error.

In other words, this works:

$ hsql -P prod --limit -1 --format md --results all --on-error stop \
    -f ./setup.sql \
    -c "select count(*) from raw_table" \
    -f ./build-models.sql \
    -c "select count(*) from modeled_table"

hsql’s exit codes are meaningful and stable:

  • 0: Success
  • 1: Query error
  • 2: Usage/config error
  • 3: Connection error
  • 4: Timeout
  • 130: Interrupted

You can also use --stats and jq together to error on a truncated query:

$ hsql --limit 100 -c "select * from orders" --csv -o data.csv --stats 2>&1 | jq -e '.truncated | not' > /dev/null