$ wc -l big1.txt big2.txt big3.txt 
 3515200 big1.txt
 3515200 big2.txt
 3515200 big3.txt
10545600 total

$ time bash llil_sql_imp2 hash2.db big1.txt big2.txt big3.txt
Importing big1.txt
Importing big2.txt
Importing big3.txt

real  0m4.350s
user  0m4.298s
sys   0m0.049s

$ time bash llil_sql_qry2 hash2.db >out.txt

real  0m9.668s
user  0m9.537s
sys   0m0.122s

$ ls -lh hash2.db 
-rw-r--r-- 1 mario mario 160M Feb  7 22:57 hash2.db

##</code><code>##

$ time ./linux-q -T "select name, sum(value) from hash.db:::kv_store group by name order by sum(value) desc, name" >out.txt

real  0m49.136s
user  0m48.667s
sys   0m0.423s

##</code><code>##

#!/usr/bin/env bash
# https://perlmonks.org/?node_id=11150232

# SQLite llil import script.
# Usage: bash llil_sql_imp2 [-reset] hash2.db big1.txt big2.txt big3.txt

# SQL

function make_script () {

  read -r -d '' var << 'EOF'

-- Set SQLite pragmas.
--
.output /dev/null
PRAGMA cache_size   = 10000;
PRAGMA page_size    = 4096;
PRAGMA journal_mode = OFF;
PRAGMA synchronous  = OFF;
PRAGMA temp_store   = MEMORY;
.output

-- Create the kv_store table.
--
CREATE TABLE IF NOT EXISTS "kv_store" (
  "name"   TEXT NOT NULL,
  "value"  INTEGER DEFAULT 0
);

-- Import CSV/TXT file(s).
--
.mode csv
.headers off
.separator ROW "\n"
.separator "\t"
EOF

  echo "$var"
}

# RUN

if [[ "$1" == "-reset" ]]; then
  DB="$2"; shift; shift
  rm -fr "$DB" "$DB"-journal "$DB"-shm "$DB"-wal
else
  DB="$1"; shift
fi

if [[ ! "$DB" =~ .db$ ]]; then
  echo "usage: bash $0 [ -reset ] hash2.db [ in1.txt ... ]" >&2
  exit 1
fi

SQLCMND=$( command -v sqlite3 )

if [[ -z "$SQLCMND" ]]; then
  echo "sqlite3: command not found" >&2
  exit 1
fi

SQLSCRIPT="$( make_script )"

NL=$'\n'

for infile in "$@"; do
  if [[ ! -r "$infile" ]]; then
    echo "$infile: cannot open '$infile', skipping..." >&2
    continue
  fi
  SQLSCRIPT+="${NL}.print Importing ${infile}"
  SQLSCRIPT+="${NL}.import '${infile}' kv_store"
done

exec "$SQLCMND" "$DB" < <(echo "$SQLSCRIPT")

##</code><code>##

#!/usr/bin/env bash
# https://perlmonks.org/?node_id=11150232

# SQLite llil query script.
# Usage: bash llil_sql_qry2 hash2.db > out.txt

# SQL

function make_script () {

  read -r -d '' var << 'EOF'

-- Set SQLite pragmas.
--
.output /dev/null
PRAGMA cache_size   = 10000;
PRAGMA page_size    = 4096;
PRAGMA journal_mode = OFF;
PRAGMA synchronous  = OFF;
PRAGMA temp_store   = MEMORY;
.output

-- Output records.
--
.mode csv
.headers off
.separator ROW "\n"
.separator "\t"

SELECT "name", sum("value") FROM "kv_store"
  GROUP BY "name"
  ORDER BY sum("value") DESC, "name";

EOF

  echo "$var"
}

# RUN

DB="$1"; shift

if [[ ! "$DB" =~ .db$ ]]; then
  echo "usage: bash $0 hash2.db" >&2
  exit 1
elif [[ ! -r "$DB" ]]; then
  echo "$DB: cannot open '$DB' (No such file)" >&2
  exit 1
fi

SQLCMND=$( command -v sqlite3 )

if [[ -z "$SQLCMND" ]]; then
  echo "sqlite3: command not found" >&2
  exit 1
fi

SQLSCRIPT="$( make_script )"

exec "$SQLCMND" "$DB" < <(echo "$SQLSCRIPT")