function insert(data, columns, table, capSQL) {

    if (!data || typeof data !== 'object') {
        throw new TypeError('Invalid parameter \'data\' specified.');
    }

    const isArray = Array.isArray(data);

    if (isArray && !data.length) {
        throw new TypeError('Cannot generate an INSERT from an empty array.');
    }

    if (columns instanceof ColumnSet) {
        if (npm.utils.isNull(table)) {
            table = columns.table;
        }
    } else {
        if (isArray && npm.utils.isNull(columns)) {
            throw new TypeError('Parameter \'columns\' is required when inserting multiple records.');
        }
        columns = new ColumnSet(columns || data);
    }

    if (!columns.columns.length) {
        throw new Error('Cannot generate an INSERT without any columns.');
    }

    if (!table) {
        throw new Error('Table name is unknown.');
    }

    if (!(table instanceof TableName)) {
        table = new TableName(table);
    }

    let query = capSQL ? sql.capCase : sql.lowCase;
    const fmOptions = {capSQL};

    const format = npm.formatting.as.format;
    query = format(query, [table.name, columns.names], fmOptions);

    if (isArray) {
        return query + data.map((d, index) => {
            if (!d || typeof d !== 'object') {
                throw new Error(`Invalid insert object at index ${index}.`);
            }
            return '(' + format(columns.variables, columns.prepare(d), fmOptions) + ')';
        }).join();
    }
    return query + '(' + format(columns.variables, columns.prepare(data), fmOptions) + ')';
}
@method helpers.insert
@description
Generates an `INSERT` query for either one object or an array of objects.

@param {object|object[]} data
An insert object with properties for insert values, or an array of such objects.

When `data` is not a non-null object and not an array, it will throw {@link external:TypeError TypeError} = `Invalid parameter 'data' specified.`

When `data` is an empty array, it will throw {@link external:TypeError TypeError} = `Cannot generate an INSERT from an empty array.`

When `data` is an array that contains a non-object value, the method will throw {@link external:Error Error} =
`Invalid insert object at index N.`

@param {array|helpers.Column|helpers.ColumnSet} [columns]
Set of columns to be inserted.

It is optional when `data` is a single object, and required when `data` is an array of objects. If not specified for an array
of objects, the method will throw {@link external:TypeError TypeError} = `Parameter 'columns' is required when inserting multiple records.`

When `columns` is not a {@link helpers.ColumnSet ColumnSet} object, a temporary {@link helpers.ColumnSet ColumnSet}
is created - from the value of `columns` (if it was specified), or from the value of `data` (if it is not an array).

When the final {@link helpers.ColumnSet ColumnSet} is empty (no columns in it), the method will throw
{@link external:Error Error} = `Cannot generate an INSERT without any columns.`

@param {helpers.TableName|Table|string} [table]
Destination table.

It is normally a required parameter. But when `columns` is passed in as a {@link helpers.ColumnSet ColumnSet} object
with `table` set in it, that will be used when this parameter isn't specified. When neither is available, the method
will throw {@link external:Error Error} = `Table name is unknown.`

@returns {string}
An `INSERT` query string.

@see
 {@link helpers.Column Column},
 {@link helpers.ColumnSet ColumnSet},
 {@link helpers.TableName TableName}

@example

const pgp = require('pg-promise')({
   capSQL: true // if you want all generated SQL capitalized
});
const {insert} = pgp.helpers;

const dataSingle = {val: 123, msg: 'hello'};
const dataMulti = [{val: 123, msg: 'hello'}, {val: 456, msg: 'world!'}];

// Column details can be taken from the data object:

insert(dataSingle, null, 'my-table');
//=> INSERT INTO "my-table"("val","msg") VALUES(123,'hello')

@example

// Column details are required for a multi-row `INSERT`:
const {insert} = pgp.helpers;

insert(dataMulti, ['val', 'msg'], 'my-table');
//=> INSERT INTO "my-table"("val","msg") VALUES(123,'hello'),(456,'world!')

@example

// Column details from a reusable ColumnSet (recommended for performance):
const {ColumnSet, insert} = pgp.helpers;

const cs = new ColumnSet(['val', 'msg'], {table: 'my-table'});

insert(dataMulti, cs);
//=> INSERT INTO "my-table"("val","msg") VALUES(123,'hello'),(456,'world!')