List values

2 snippets across 2 stacks — Bash & Linux, SQL

Also written as list of values

SHBash & Linux

Arrays

syntax

arr=(val1 val2 val3)
${arr[0]}  ${arr[@]}  ${#arr[@]}

example

SERVERS=("web01.prod" "web02.prod" "db01.prod")
echo "First: ${SERVERS[0]}"
echo "All: ${SERVERS[@]}"
echo "Count: ${#SERVERS[@]}"

SERVERS+=("cache01.prod")

for srv in "${SERVERS[@]}"; do
  ssh deploy@"${srv}" 'uptime'
done

output

First: web01.prod
All: web01.prod web02.prod db01.prod
Count: 3

Note Indices start at 0. Always quote "${arr[@]}" to preserve elements with spaces. ${#arr[@]} gives the length. += appends. unset 'arr[1]' removes an element (but does not reindex). Bash arrays are not available in sh/POSIX shell.

SQLSQL

STRING_AGG / GROUP_CONCAT

SQL · Aggregation

syntax

-- PostgreSQL / ANSI
STRING_AGG(column, delimiter)
-- MySQL
GROUP_CONCAT(column SEPARATOR delimiter)

example

-- PostgreSQL
SELECT
  order_id,
  STRING_AGG(product_name, ', ' ORDER BY product_name) AS products
FROM order_items oi
JOIN products p ON p.id = oi.product_id
GROUP BY order_id;

output

-- order_id | products
-- 101      | Keyboard, Monitor, Mouse

Note STRING_AGG is standard SQL. MySQL uses GROUP_CONCAT with a default max length of 1024 characters — increase group_concat_max_len if results get truncated.