# Splitting and joining strings

These functions split text into arrays or rows and join array members back into text. Choose literal-delimiter functions when the separator is fixed, and regular-expression variants when the separator is a pattern.

Empty separators, NULL inputs and NULL array members have function-specific behavior. `array_to_string` can supply an explicit replacement for missing members.

## Example: Changing a list separator

```sql
SELECT array_to_string(string_to_array('Ada,Grace,Linus', ','), ' | ')
FORMAT csv;
```

```text
"Ada | Grace | Linus"
```

## array_to_string

Join native array members in depth-first order, skipping NULL unless a replacement is supplied.

### Syntax

```text
array_to_string(array, delimiter[, null_string])
```

### Arguments

Native Array, delimiter text, optional NULL-member replacement; nested arrays are flattened.

### Returned value

TEXT; empty array gives empty text; NULL array or delimiter gives NULL.

### Example

```sql
SELECT array_to_string(array(1,NULL,2),',','?') FORMAT csv;
```

```text
"1,?,2"
```

## regexp_split_to_array

Split text into native text fields using a Unicode regex delimiter.

### Syntax

```text
regexp_split_to_array(text, pattern[, flags])
```

### Arguments

Existing regex syntax/flags; ignore zero-length delimiters at endpoints and immediately after a preceding match; captures are excluded.

### Returned value

Native Array(String); empty source produces one empty field; NULL propagates.

### Example

```sql
SELECT array_to_string(regexp_split_to_array('a b c',' +'),'|') FORMAT csv;
```

```text
"a|b|c"
```

## regexp_split_to_table

Split text into rows using the documented delimiter rules.

### Syntax

```text
FROM regexp_split_to_table(text, pattern[, flags])
```

### Arguments

Same separators and flags as regexp_split_to_array; any NULL argument emits no rows.

### Returned value

One TEXT field per row in column regexp_split_to_table; FROM-only.

### Example

```sql
SELECT * FROM regexp_split_to_table('a,b',',') FORMAT csv;
```

```text
"a"
"b"
```

## split_part

Return one delimiter-separated field from text.

### Syntax

```text
split_part(value, delimiter, field)
```

### Arguments

Positive fields count from one; negative fields count from the last field; zero raises INVALID_ARGUMENT. Empty delimiter leaves one field.

### Returned value

Field TEXT, empty TEXT when missing, or NULL for any NULL argument.

### Example

```sql
SELECT split_part('a::b::c','::',2) FORMAT csv;
```

```text
"b"
```

## string_to_array

Split text into a native Array(String), replacing exact null_string fields with NULL.

### Syntax

```text
string_to_array(text, delimiter[, null_string])
```

### Arguments

NULL delimiter splits Unicode characters; empty delimiter retains one field; empty input gives an empty array.

### Returned value

Native text array; nullable members when a non-NULL null_string is supplied; NULL for NULL input.

### Example

```sql
SELECT array_to_string(string_to_array('a,b,c',','),'|') FORMAT csv;
```

```text
"a|b|c"
```

## string_to_table

Split text into rows using the documented delimiter rules.

### Syntax

```text
FROM string_to_table(text,delimiter[,null_string])
```

### Arguments

NULL delimiter splits Unicode characters; empty delimiter keeps the whole nonempty input; optional marker yields SQL NULL; empty source yields zero rows.

### Returned value

One string_to_table column containing nullable TEXT.

### Example

```sql
SELECT * FROM string_to_table('a,b',',') FORMAT csv;
```

```text
"a"
"b"
```