--- title: SQL Connectors pagination_prev: demos/cli/index pagination_next: demos/local/index sidebar_custom_props: sql: true --- import Tabs from '@theme/Tabs'; import TabItem from '@theme/TabItem'; Structured Query Language ("SQL") is a popular declarative language for issuing commands to database servers. ## Raw SQL Operations ### Generating Tables This example will fetch https://sheetjs.com/data/cd.xls, scan the columns of the first worksheet to determine data types, and generate 6 PostgreSQL statements.
Explanation (click to show) The relevant `generate_sql` function takes a worksheet name and a table name: ```js // define mapping between determined types and PostgreSQL types const PG = { "n": "float8", "s": "text", "b": "boolean" }; function generate_sql(ws, wsname) { // generate an array of objects from the data const aoo = XLSX.utils.sheet_to_json(ws); // types will map column headers to types, while hdr holds headers in order const types = {}, hdr = []; // loop across each row object aoo.forEach(row => // Object.entries returns a row of [key, value] pairs. Loop across those Object.entries(row).forEach(([k,v]) => { // If this is first time seeing key, mark unknown and append header array if(!types[k]) { types[k] = "?"; hdr.push(k); } // skip null and undefined if(v == null) return; // check and resolve type switch(typeof v) { case "string": // strings are the broadest type types[k] = "s"; break; case "number": // if column is not string, number is the broadest type if(types[k] != "s") types[k] = "n"; break; case "boolean": // only mark boolean if column is unknown or boolean if("?b".includes(types[k])) types[k] = "b"; break; default: types[k] = "s"; break; // default to string type } }) ); // The final array consists of the CREATE TABLE query and a series of INSERTs return [ // generate CREATE TABLE query and return batch `CREATE TABLE \`${wsname}\` (${hdr.map(h => // column name must be wrapped in backticks `\`${h}\` ${PG[types[h]]}` ).join(", ")});` ].concat(aoo.map(row => { // generate INSERT query for each row // entries will be an array of [key, value] pairs for the data in the row const entries = Object.entries(row); // fields will hold the column names and values will hold the values const fields = [], values = []; // check each key/value pair in the row entries.forEach(([k,v]) => { // skip null / undefined if(v == null) return; // column name must be wrapped in backticks fields.push(`\`${k}\``); // when the field type is numeric, `true` -> 1 and `false` -> 0 if(types[k] == "n") values.push(typeof v == "boolean" ? (v ? 1 : 0) : v); // otherwise, else values.push(`'${v.toString().replaceAll("'", "''")}'`); }) if(fields.length) return `INSERT INTO \`${wsname}\` (${fields.join(", ")}) VALUES (${values.join(", ")})`; })).filter(x => x); // filter out skipped rows } ```
```jsx live function SheetJSQLWriter() { // define mapping between determined types and PostgreSQL types const PG = { "n": "float8", "s": "text", "b": "boolean" }; function generate_sql(ws, wsname) { const aoo = XLSX.utils.sheet_to_json(ws); const types = {}, hdr = []; // loop across each key in each column aoo.forEach(row => Object.entries(row).forEach(([k,v]) => { // set up type if header hasn't been seen if(!types[k]) { types[k] = "?"; hdr.push(k); } // check and resolve type switch(typeof v) { case "string": types[k] = "s"; break; case "number": if(types[k] != "s") types[k] = "n"; break; case "boolean": if("?b".includes(types[k])) types[k] = "b"; break; default: types[k] = "s"; break; } })); return [ // generate CREATE TABLE query and return batch `CREATE TABLE \`${wsname}\` (${hdr.map(h => `\`${h}\` ${PG[types[h]]}`).join(", ")});` ].concat(aoo.map(row => { const entries = Object.entries(row); const fields = [], values = []; entries.forEach(([k,v]) => { if(v == null) return; fields.push(`\`${k}\``); if(types[k] == "n") values.push(typeof v == "boolean" ? (v ? 1 : 0) : v); else values.push(`'${v.toString().replaceAll("'", "''")}'`); }) if(fields.length) return `INSERT INTO \`${wsname}\` (${fields.join(", ")}) VALUES (${values.join(", ")})`; })).filter(x => x).slice(0, 6); } const [url, setUrl] = React.useState("https://sheetjs.com/data/cd.xls"); const set_url = (evt) => setUrl(evt.target.value); const [out, setOut] = React.useState(""); const xport = React.useCallback(async() => { const ab = await (await fetch(url)).arrayBuffer(); const wb = XLSX.read(ab), wsname = wb.SheetNames[0]; setOut(generate_sql(wb.Sheets[wsname], wsname).join("\n")); }); return ( <> {out && ( <>{url}
{out}
)} URL:
); } ``` ## Databases ### Query Builders Query builders are designed to simplify query generation and normalize field types and other database minutiae. **Knex** **[The exposition has been moved to a separate page.](/docs/demos/data/knex)** ### Other SQL Databases The `generate_sql` function from ["Generating Tables"](#generating-tables) can be adapted to generate SQL statements for a variety of databases, including: **PostgreSQL** **[The exposition has been moved to a separate page.](/docs/demos/data/postgresql)** **MySQL / MariaDB** **[The exposition has been moved to a separate page.](/docs/demos/data/mariadb)**