docs.sheetjs.com/docz/docs/03-demos/23-data/16-postgresql.md

---
title: Sheets with PostgreSQL
sidebar_label: PostgreSQL
pagination_prev: demos/cli/index
pagination_next: demos/local/index
sidebar_custom_props:
  sql: true
---

import current from '/version.js';
import CodeBlock from '@theme/CodeBlock';

[PostgreSQL](https://postgresql.org/) (colloquially referenced as "Postgres") is
an open source object-relational database system.

[SheetJS](https://sheetjs.com) is a JavaScript library for reading and writing
data from spreadsheets.

This demo uses SheetJS to exchange data between spreadsheets and PostgreSQL
databases. We'll explore how to save tables from a database to spreadsheets and
how to add data from spreadsheets into a database.

:::caution pass

**It is strongly recommended to use PostgreSQL with a query builder or ORM.**

While it is possible to generate SQL statements directly, there are many subtle
details and pitfalls. Battle-tested solutions generally provide mitigations
against SQL injection and other vulnerabilities.

:::

:::note Tested Deployments

This demo was tested in the following environments:

| Postgres | Connector Library | Date       |
|:---------|:------------------|:-----------|
| `16.6.1` | `pg` (`8.13.1`)   | 2024-12-03 |
| `15.6`   | `pg` (`8.11.4`)   | 2024-03-31 |
| `14.11`  | `pg` (`8.11.4`)   | 2024-03-31 |

:::

## Integration Details

The [SheetJS NodeJS module](/docs/getting-started/installation/nodejs) can be
loaded in NodeJS scripts that connect to PostgreSQL databases.

This demo uses the `pg` connector module[^1], but the same mechanics apply to
other PostgreSQL libraries.

### Exporting Data

`Client#query` returns a Promise that resolves to a result set. The `rows`
property of the result is an array of objects.

The SheetJS `json_to_sheet` method[^2] can generate a worksheet object[^3] from
the array of objects:

```js
const table_name = "Tabeller1"; // name of table

/* fetch all data from specified table */
const res = await client.query(`SELECT * FROM ${table_name}`);

/* generate a SheetJS worksheet object from the data */
const worksheet = XLSX.utils.json_to_sheet(res.rows);
```

A workbook object can be built from the worksheet using utility functions[^4].
The workbook can be exported using the SheetJS `writeFile` method[^5]:

```js
/* create a new workbook and add the worksheet */
const wb = XLSX.utils.book_new();
XLSX.utils.book_append_sheet(wb, worksheet, "Sheet1");

/* export workbook to XLSX */
XLSX.writeFile(wb, "SheetJSPGExport.xlsx");
```

### Importing Data

The SheetJS `sheet_to_json` function[^6] takes a worksheet object and generates
an array of objects.

Queries must be manually generated from the objects. Assuming the field names
in the object match the column headers, a loop can generate `INSERT` queries.

:::danger pass

**PostgreSQL does not allow parameterized queries with variable column names**

```sql
INSERT INTO table_name (?) VALUES (?);
-- ---------------------^ variable column names are not valid
```

Queries are generated manually. To help prevent SQL injection vulnerabilities,
the `pg-format`[^7] module escapes identifiers and fields.

:::

```js
/* generate an array of arrays from the worksheet */
const aoo = XLSX.utils.sheet_to_json(ws);

const table_name = "Blatte1"; // name of table

/* loop through the data rows */
for(let row of aoo) {

  /* generate format helper strings */
  const ent = Object.entries(row);
  const Istr = Array.from({length: entries.length}, ()=>"%I").join(", ");
  const Lstr = Array.from({length: entries.length}, ()=>"%L").join(", ");

  /* generate INSERT statement */
  let query = format.withArray(
    `INSERT INTO %I (${Istr}) VALUES(${Lstr})`,
    [ table_name, ...ent.map(x => x[0]), ...ent.map(x => x[1]) ]
  );

  /* execute INSERT statement */
  await client.query(query);
}
```

### Creating a Table

The worksheet can be scanned to determine column names and types. With the names
and types, a `CREATE TABLE` query can be written.

<details>
  <summary><b>Implementation Details</b> (click to show)</summary>

The `sheet_to_pg_table` function:

- scans worksheet cells to determine column names and types
- drops and creates a new table with the determined column names and types
- loads the entire dataset into the new table

```js
/* create table and load data given a worksheet and a PostgreSQL client */
async function sheet_to_pg_table(client, worksheet, tableName) {
    if (!worksheet['!ref']) return;

    const range = XLSX.utils.decode_range(worksheet['!ref']);

    /* Extract headers from first row, clean names for PostgreSQL */
    const headers = [];
    for (let col = range.s.c; col <= range.e.c; col++) {
        const cellAddress = XLSX.utils.encode_cell({ r: range.s.r, c: col });
        const cell = worksheet[cellAddress];
        const headerValue = cell ? String(cell.v).replace(/[^a-zA-Z0-9_]/g, '_') : `column_${col + 1}`;
        headers.push(headerValue.toLowerCase());
    }

    /* Group cell values by column for type deduction */
    const columnValues = headers.map(() => []);
    for (let row = range.s.r + 1; row <= range.e.r; row++) {
        for (let col = range.s.c; col <= range.e.c; col++) {
            const cellAddress = XLSX.utils.encode_cell({ r: row, c: col });
            const cell = worksheet[cellAddress];
            columnValues[col].push(cell);
        }
    }

    /* Deduce PostgreSQL type for each column */
    const types = {};
    headers.forEach((header, idx) => {
        types[header] = deduceType(columnValues[idx]);
    });

    /* Delete table if it exists in the DB */
    await client.query(format('DROP TABLE IF EXISTS %I', tableName));

    /* Create table */
    const createTableSQL = format(
        'CREATE TABLE %I (%s)',
        tableName,
        headers.map(header => format('%I %s', header, types[header])).join(', ')
    );
    await client.query(createTableSQL);

    /* Insert data row by row */
    for (let row = range.s.r + 1; row <= range.e.r; row++) {
        const values = headers.map((header, col) => {
            const cellAddress = XLSX.utils.encode_cell({ r: row, c: col });
            const cell = worksheet[cellAddress];
            return parseValue(cell, types[header]);
        });

        const insertSQL = format(
            'INSERT INTO %I (%s) VALUES (%s)',
            tableName,
            headers.map(h => format('%I', h)).join(', '),
            values.map(() => '%L').join(', ')
        );
        await client.query(format(insertSQL, ...values));
    }
}

function deduceType(cells) {
    if (!cells || cells.length === 0) return 'text';

    const nonEmptyCells = cells.filter(cell => cell && cell.v != null);
    if (nonEmptyCells.length === 0) return 'text';

    // Check for dates by looking at both cell type and formatted value
    const isDateCell = cell => cell?.t === 'd' || (cell?.t === 'n' && cell.w && /\d{4}-\d{2}-\d{2}|\d{1,2}\/\d{1,2}\/\d{4}|\d{2}-[A-Za-z]{3}-\d{4}|[A-Za-z]{3}-\d{2}|\d{1,2}-[A-Za-z]{3}/.test(cell.w));

    if (nonEmptyCells.some(isDateCell)) { return 'date'; }

    const allBooleans = nonEmptyCells.every(cell => cell.t === 'b');
    if (allBooleans) { return 'boolean'; }

    const allNumbers = nonEmptyCells.every(cell => cell.t === 'n' || (cell.t === 's' && !isNaN(cell.v.replace(/[,$\s%()]/g, ''))));

    if (allNumbers) {
        const numbers = nonEmptyCells.map(cell => {
            if (cell.t === 'n') return cell.v;
            return parseFloat(cell.v.replace(/[,$\s%()]/g, ''));
        });

        const needsPrecision = numbers.some(num => {
            const str = num.toString();
            return str.includes('e') ||
                   (str.includes('.') && str.split('.')[1].length > 6) ||
                   Math.abs(num) > 1e15;
        });

        return needsPrecision ? 'numeric' : 'double precision';
    }
    return 'text';
}

function parseValue(cell, type) {
    if (!cell || cell.v == null) return null;

    switch (type) {
        case 'date':
            if (cell.t === 'd') { return cell.v.toISOString().split('T')[0]; }
            if (cell.t === 'n') {
                const date = new Date((cell.v - 25569) * 86400 * 1000);
                return date.toISOString().split('T')[0];
            }
            return null;

        case 'numeric':
        case 'double precision':
            if (cell.t === 'n') return cell.v;
            if (cell.t === 's') {
                const cleaned = cell.v.replace(/[,$\s%()]/g, '');
                if (!isNaN(cleaned)) return parseFloat(cleaned);
            }
            return null;

        case 'boolean':
            return cell.t === 'b' ? cell.v : null;

        default:
            return String(cell.v);
    }
}
```

</details>


## Complete Example

0) Install and start the PostgreSQL server.

<details>
  <summary><b>Installation Notes</b> (click to show)</summary>

On macOS, install the `postgresql` formula with Homebrew:

```bash
brew install postgresql@16
```

The last few lines of the installer explain how to start the database:

```text
Or, if you don't want/need a background service you can just run:
// highlight-next-line
  LC_ALL="C" /usr/local/opt/postgresql@16/bin/postgres -D /usr/local/var/postgresql@16
```

On Linux, install `postgresql` by running the following script:

```bash
echo "deb http://apt.postgresql.org/pub/repos/apt $(lsb_release -cs)-pgdg main" | sudo tee /etc/apt/sources.list.d/pgdg.list
wget -qO - https://www.postgresql.org/media/keys/ACCC4CF8.asc | sudo apt-key add -

sudo apt update
sudo apt install postgresql-16
sudo systemctl start postgresql

# Optional: Create user with password
sudo -u postgres createuser -P $USER
sudo -u postgres psql -c "ALTER USER $USER WITH SUPERUSER;"
```

If running the optional user creation steps above, a PostgreSQL password will be required. [^8]

Run the command to start a local database instance.

</details>

1) Drop any existing database with the name `SheetJSPG`:

```bash
dropdb SheetJSPG
```

:::caution pass

Some Linux installations do not create the `dropdb` command. The command can be
run through the `postgres` command-line tool:

```bash title="dropdb in Ubuntu/Debian"
sudo -i -u postgres dropdb SheetJSPG
```

:::

:::info pass

If the server is running elsewhere, or if the username is different from the
current user, command-line flags can override the defaults.

| Option        | Explanation
|:--------------|:--------------------------|
| `-h HOSTNAME` | Name of the server        |
| `-p PORT`     | specifies the port number |
| `-U USERNAME` | specifies the username    |

:::

:::note pass

If the database does not exist, the command will fail with the following error:

```
dropdb: error: database removal failed: ERROR:  database "SheetJSPG" does not exist
```

This error can be safely ignored.

:::

2) Create an empty `SheetJSPG` database using the `createdb` command:

```bash
createdb SheetJSPG
```

:::caution pass

Some Linux installations do not create the `createdb` command. The command can be
run through the `postgres` command-line tool:

```bash title="createdb in Ubuntu/Debian"
sudo -i -u postgres createdb SheetJSPG
```

:::

:::note pass

`createdb` supports the same `-h`, `-p`, and `-U` flags as `dropdb`.

:::

### Connector Test

3) Create a project folder:

```bash
mkdir sheetjs-pg
cd sheetjs-pg
npm init -y
```

4) Install the `pg` connector module:

```bash
npm i --save pg@8.13.1
```

5) Save the following example codeblock to `PGTest.js`:

```js title="PGTest.js"
const pg = require("pg");
const client = new pg.Client({
  database:"SheetJSPG",
// highlight-start
  host: "127.0.0.1", // localhost
  port: 5432,
  //user: "",
  //password: ""
// highlight-end
});
(async() => {

await client.connect();
const res = await client.query('SELECT $1::text as message', ['Hello world!']);
console.log(res.rows[0].message); // Hello world!
await client.end();

})();
```

6) Edit the new `PGTest.js` script and modify the highlighted lines from the
codeblock to reflect the database deployment settings.

The settings in the codeblock match the default configuration for macOS Homebrew
PostgreSQL server. For other deployments:

- If the server is not running on your computer, set `host` and `port` to the
correct host name and port number.

- If the server expects a different username and password, uncomment the `user`
and `password` lines and replace the values with the username and password.

- For Ubuntu/Debian PostgreSQL installations, the default user is `postgres`. The password must be set during installation or using `sudo -u postgres psql` followed by  `\password postgres` in the psql prompt.

7) Run the script:

```bash
node PGTest.js
```

It should print `Hello world!`

:::caution pass

If the output is not `Hello world!` or if there is an error, please report the
issue to the `pg` connector project for further diagnosis.

:::

### Add SheetJS

8) Install dependencies:

<CodeBlock language="bash">{`\
npm i --save https://cdn.sheetjs.com/xlsx-${current}/xlsx-${current}.tgz pg-format@1.0.4`}
</CodeBlock>

9) Download [`SheetJSPG.js`](pathname:///postgresql/SheetJSPG.js):

```bash
curl -LO https://docs.sheetjs.com/postgresql/SheetJSPG.js
```

This script will:
- read and parse the test file `pres.numbers`
- create a connection to the `SheetJSPG` database on a local PostgreSQL server
- load data from the first worksheet into a table with name `Presidents`
- disconnect and reconnect to the database
- dump data from the table `Presidents`
- export the dataset to `SheetJSPG.xlsx`

10) Edit the `SheetJSPG.js` script.

The script defines an `opts` object:

```js title="SheetJSPG.js (configuration lines)"
const XLSX = require("xlsx");
const opts = {
  database:"SheetJSPG",
// highlight-start
  host: "127.0.0.1", // localhost
  port: 5432,
  //user: "",
  //password: ""
// highlight-end
};
```

The settings in the codeblock match the default configuration for macOS Homebrew
PostgreSQL server. For other deployments:

- If the server is not running on your computer, set `host` and `port` to the
correct host name and port number.

- If the server expects a different username and password, uncomment the `user`
and `password` lines and replace the values with the username and password.

- For Ubuntu/Debian PostgreSQL installations, the default user is postgres. The password must be set during installation or using sudo -u postgres psql followed by \password postgres in the psql prompt.


11) Fetch the example file [`pres.numbers`](https://docs.sheetjs.com/pres.numbers):

```bash
curl -L -O https://docs.sheetjs.com/pres.numbers
```

12) Run the script:

```bash
node SheetJSPG.js
```

13) Verify the result:

- `SheetJSPGExport.xlsx` can be opened in a spreadsheet app or tested in the terminal

```bash
npx xlsx-cli SheetJSPGExport.xlsx
```

- The database server can be queried using the `psql` command line tool.

If the server is running locally, the command will be:

```bash
psql SheetJSPG -c 'SELECT * FROM "Presidents";'
```

:::note pass

`psql` supports the same `-h`, `-p`, and `-U` flags as `dropdb` and `createdb`.

:::


[^1]: See [the official `pg` website](https://node-postgres.com/) for more info.
[^2]: See [`json_to_sheet` in "Utilities"](/docs/api/utilities/array#array-of-objects-input)
[^3]: See ["Sheet Objects"](/docs/csf/sheet) in "SheetJS Data Model" for more details.
[^4]: See ["Workbook Helpers" in "Utilities"](/docs/api/utilities/wb) for details on `book_new` and `book_append_sheet`.
[^5]: See [`writeFile` in "Writing Files"](/docs/api/write-options)
[^6]: See [`sheet_to_json` in "Utilities"](/docs/api/utilities/array#array-output)
[^7]: The [`pg-format`](https://npm.im/pg-format) package is available on the public NPM registry. Even though the project is marked as deprecated, the official [`pg` website still recommends `pg-format`](https://node-postgres.com/features/queries#parameterized-query:~:text=use%20pg%2Dformat%20package%20for%20handling%20escaping)
[^8]: PostgreSQL on Linux uses [SCRAM authentication by default, which requires a password](https://www.postgresql.org/docs/current/auth-password.html)